I think that Emboar should be moved back from Low S to Top A or even Mid A.  After playing with and against so many Emboars since it rised from NU, I admit that it is an really really good pokemon.  It's cool typing helps it to check grass types, Escavalier, Durant, Absol and others in only one slot is really invaluable for offensive teams.  It's choice scarf set is one of the best revenge killers in the tier, while CB and Mixed sets are great wallbreakers.  However, there are quite some flaws for it stopping it from performing its job perfectly.
The choice scarf set is currently Emboar's best set and the set causes it to be argued to be S rank.  However, every time I'm using it, I just feel that I need to bring another check for the pokemon it 'covers' due to how fast it being worn down.  110/65/65 defenses are cool, but not too much an upgrade from Darmanitan's 105/55/55, which is considered being extremely frail in UU.  It's secondary fighting typing gives it stealth rock neutrality, but in fact how much it has to switch in causes it to be worn down by SR and spikes over time until it is being overwhelmed by the pokes it is supposed to check.  Not to mention Flare Blitz and Wild Charge's heavy recoil.  Playing against it is usually not difficult if you have any bulky water types since it cannot hurt any of them.  These are some calcs showing actually situations.
When Emboar tries to revenge something AND predicts well for a switch:
252 Atk Emboar Wild Charge vs. 248 HP / 144 Def Slowking: 192-228 (48.85 - 58.01%) -- 57.81% chance to 2HKO
Slowking just switches out and recover health via Regenerator, Emboar takes damage when switching in and recoil.
252 Atk Emboar Wild Charge vs. 252 HP / 252+ Def Poliwrath: 142-168 (36.97 - 43.75%) -- 99.83% chance to 3HKO
Great! 3HKO with a supper effective hit!
-1 252 Atk Emboar Wild Charge vs. 252 HP / 240+ Def Qwilfish: 112-132 (33.53 - 39.52%) -- 23.19% chance to 3HKO
Qwilfish: Hi Emboar, i'm setting up spikes and pain splitting on your face.  Maybe I can also fire off a T-wave too.
252 Atk Emboar Wild Charge vs. 104 HP / 252+ Def Alomomola: 158-186 (31.79 - 37.42%) -- guaranteed 4HKO
Alomomola: I can beat you even i'm asleep...
252 Atk Emboar Superpower vs. 248 HP / 252+ Def Quagsire: 151-178 (38.42 - 45.29%) -- guaranteed 3HKO
Quasire: I'm bad, you're worse
These are all exellent pokemons in RU (except Quagsire lol) and are all able to hard counter Emboar, gaining free momentum every time Emboar tries to revenge things, causing Emboar to take hazard damage every time it switches in.  Beside these hard counters, things like Druddigon, Rhydon, Aggron, Kabutops, Omastar, Uxie, Moltres, Golurk etc. are all great pokemons and can check Emboar locked into some of its moves.  Eventually, it will be overwhelmed by the pokemons it is supposed to check.
Against Escavalier:
252+ Atk Choice Band Escavalier Megahorn vs. 0 HP / 0 Def Emboar: 117-138 (32.4 - 38.22%) -- 98.63% chance to 3HKO
252+ Atk Choice Band Swarm Escavalier Megahorn vs. 0 HP / 0 Def Emboar: 176-208 (48.75 - 57.61%) -- 94.92% chance to 2HKO
252+ Atk Choice Band Escavalier Iron Head vs. 0 HP / 0 Def Emboar: 156-185 (43.21 - 51.24%) -- 98.83% chance to 2HKO after Stealth Rock
252+ Atk Choice Band Escavalier Return vs. 0 HP / 0 Def Emboar: 267-315 (73.96 - 87.25%) -- 81.25% chance to OHKO after Stealth Rock and Spikes
Despite its resistance to every move Escavalier has, Emboar can only really switch into Escavalier once that's not using Megahorn not in Swarm range.  Obviously, Escavalier is most likely to spam Megahorn and isn't commonly in Swarm range while Emboar outspeeds and Ko it first, but Emboar is still a shaky check due to how easy Escavalier can switch in during the match and Emboar's suicidal nature.
Against Durant:
252 Atk Life Orb Hustle Durant X-Scissor vs. 0 HP / 0 Def Emboar: 79-94 (21.88 - 26.03%) -- guaranteed 4HKO after Stealth Rock
252 Atk Life Orb Hustle Durant Iron Head vs. 0 HP / 0 Def Emboar: 160-188 (44.32 - 52.07%) -- guaranteed 2HKO after Stealth Rock
252 Atk Life Orb Hustle Durant Superpower vs. 0 HP / 0 Def Emboar: 320-377 (88.64 - 104.43%) -- guaranteed OHKO after Stealth Rock
Emboar is able to switch into X-Scissor and Hone Claws freely.  Superpower ruins it easily though and it takes heavy damage from Iron Head.  Still, it is a good check since Durant usually requires sacrifice to switch in.
Against Absol:
252+ Atk Life Orb Absol Night Slash vs. 0 HP / 0 Def Emboar: 116-136 (32.13 - 37.67%) -- 96.29% chance to 3HKO
252+ Atk Life Orb Absol Sucker Punch vs. 0 HP / 0 Def Emboar: 133-156 (36.84 - 43.21%) -- 85.94% chance to 2HKO after Stealth Rock and Spikes
252+ Atk Life Orb Absol Superpower vs. 0 HP / 0 Def Emboar: 265-313 (73.4 - 86.7%) -- 75% chance to OHKO after Stealth Rock and Spikes
Emboar is a great check to Absol since most of the time it is spamming Sucker punch while it is quite hard for Absol to switch in.  However, the Emboar user must be vary of getting hit by Superpower on the switch as well as Night Slash + Sucker Punch can deal up to 80%.
Against Sceptile:
252 SpA Life Orb Sceptile Giga Drain vs. 0 HP / 4 SpD Emboar: 97-114 (26.86 - 31.57%) -- guaranteed 4HKO
252 SpA Life Orb Overgrow Sceptile Giga Drain vs. 0 HP / 4 SpD Emboar: 144-172 (39.88 - 47.64%) -- guaranteed 3HKO
252 SpA Life Orb Sceptile Focus Blast vs. 0 HP / 4 SpD Emboar: 207-244 (57.34 - 67.59%) -- guaranteed 2HKO
252 SpA Choice Specs Sceptile Leaf Storm vs. 0 HP / 4 SpD Emboar: 208-246 (57.61 - 68.14%) -- guaranteed 2HKO
252 SpA Choice Specs Sceptile Focus Blast vs. 0 HP / 4 SpD Emboar: 238-281 (65.92 - 77.83%) -- guaranteed 2HKO
252 SpA Choice Specs Overgrow Sceptile Leaf Storm vs. 0 HP / 4 SpD Emboar: 312-368 (86.42 - 101.93%) -- 12.5% chance to OHKO
252+ Atk Flying Gem Sceptile Acrobatics (110 BP) vs. 0 HP / 0 Def Emboar: 420-496 (116.34 - 137.39%) -- guaranteed OHKO
The calcs above shows three common Sceptile sets, Sub+3 attacks, Choice Specs and SD,  Emboar is an extremely shaky check to every one of them.  The substitute set will often be under a sub when Emboar comes in, forcing it to take a LO Focus Blast while showing its choice locked move.  The Choice Specs set hits extremely hard and can even possibly OHKO Emboar with an resisted Leaf Storm when it is in Overgrow range.  The Emboar user basically has to use something to take the strong hit before sending in Emboar for the revenge kill.  Emboar is in the best position when against the SD set since most people use SD on the first turn, allowing Emboar to switch in freely.  However, Emboar is easily OHKOed by Acrobatics.  Other custom sets such as Special Attacker with Acrobatics and White Herb Leaf Storm also handles Emboar quite well.  Emboar simply isn't a good check to Sceptile.
Against Lilligant:
252 SpA Life Orb Lilligant Giga Drain vs. 0 HP / 4 SpD Emboar: 100-118 (27.7 - 32.68%) -- guaranteed 4HKO
252 SpA Life Orb Lilligant Hidden Power Rock vs. 0 HP / 4 SpD Emboar: 125-148 (34.62 - 40.99%) -- guaranteed 3HKO
+1 252 SpA Life Orb Lilligant Hidden Power Rock vs. 0 HP / 4 SpD Emboar: 187-221 (51.8 - 61.21%) -- guaranteed 2HKO
+1 252 SpA Life Orb Lilligant Petal Dance vs. 0 HP / 4 SpD Emboar: 239-282 (66.2 - 78.11%) -- guaranteed 2HKO
Emboar can take hits quite well from an unboosted Lilligant, while also having Sleep Talk to take Lilligant Sleep Power.  However, Lilligant usually won't set up early game but rather weakening the opponent's team with attacks.  There are two STAB moves of choices for Lilligant.  Obviously, Petal Dance Lilligant has a easy time against Emboar since it only needs to hit Emboar once with +0 hp rock and can sweep next time it switches in.  Giga Drain variants are usually needs some hazards to wear down Emboar, but has more early game utility with a reliable STAB move.  Emboar beats hp fire variants easily though.
Against the five most common pokemon Emboar checks, Emboar actually only does a great job against Durant and Absol and is only an okay check against the rest of them.  Coupled with scarf Emboar's inability to deal heavy damage, Emboar usually is only capable to wear down something it checks or sometimes ko one of them.  While choice scarf Emboar is cool in theory that it can check so many things in one slot, people already learned to deal with it and in reality it can hardly ko the things it needs to check.
CB and Mixed attacker Emboar share similar roles as wallbreakers.  Nearly everything in the tier is 2HKOed by it.  This seems OP, right?  Except that Moltres, Magmortar, Specs Analytic Magneton, Mixed Samurrott and so many others can accomplish the same thing.  While Emboar is hard to switch into with these two sets, its low speed, extreme recoil, average bulk and fairly exploitable weaknesses to Ground, Water, Psychic etc. make Emboar an average wallbreaker.  Obviously, it has some perks namely SR neutrality, possibly of insanely powerful Blaze Flare Blitz and accurate moves on CB set, but wallbreaker Emboar simply can't stand out of the crowd.
Emboar surely is a good pokemon in RU with its ability to check numerous threats with it Scarf set and ability to wallbreak with other sets, it is mostly only threatening on paper but many times fail in practice.  It should certainly be in Mid A or at least Top A.