This looks like a good team overall utilizing some underrated sets and team members, though it would perform better after a few fixes.
Threat(s)
Stall
Lack of Dragon- type resist
Solid team, most offensive threats seem well covered, however the team looks like it could run into a whole lot of trouble against stall; each member of this team is walled and forced out by the common Stall members: Skarmory|Blissey|Rotom-A|Hippowdon|Filler|Filler. Skarmory uses Swampert and Snorlax for set-up bait, and can render their pHazing useless. Poliwrath is in the same boat, it's also shut down by Skarmory's Taunt and pHazed, or taken on by Rotom-A and a super effective Thunderbolt or a crippling Will-O-Wisp, while not hitting too hard with Ice Punch. Your two Special Attackers in Zapdos and Togekiss are stopped cold by Blissey, and outstalled with Toxic/Soft Boiled. Finally Heracross dies to the combination of Rotom-A and Skarmory (Rest-talk Rotom-A are most commonly seen on Stall, so Toxic won't be enough). So the bottom line is, you won't be hitting Stall team hard enough and putting pressure on them, while they will get hazards up and slowly kill off this team's members. Okay, so this went unaddressed, but it seems like you have a major weakness to Dragon-types such as Dragon Dance Kingdra and Dragonite, Mixed/Scarf Flygon. These dragons can dent your team pretty hard with Draco Meteors and Outrages, while you have no safe resists to these attacks.
With that said, I think a Bulky DD Taunt Gyarados over Poliwrath is an excellent way to help against stall; To be honest, I don't see what Poliwrath is doing for your team and seems like dead weight at best. Gyarados gives you a great method to tank Physical attacks from the likes of Swords Dance Lucario and the like, who can sweep this team with a weakened Zapdos. Gyarados shuts all the main Stall members down with Taunt, from there simply grab a (or more) Dragon Dance(s) and wreck havoc. I think a spread of 156 HP / 72 Atk / 96 Def / 184 Spe with Leftovers and an Adamant nature is alright, and a moveset of Dragon Dance|Waterfall|Taunt|Bounce can work wonders for this team. Remember though, Rotom-A will still be annoying to face on stall, and I will recommend a Snorlax set that could aid you with that.
I think you could move Swampert to the lead position and switch Togekiss with Life Orb Heatran. Heatran is an excellent way to help against stall; To be honest, I don't see what Poliwrath is doing for your team and seems like dead weight at best. Heatran can shut stall down single with little to no support with the following set: Fire Blast|Earth Power|Hidden Power Grass|Explosionwith a Life Orb and Naive nature. With Taunt, you shut down Heatran's worst enemy, Blissey, and it will have the choice to either die to repeated Fire Blasts or switch. Skarmory and Rotom-A don't like a STAB LO Fire Blast to the face, Heatran is definitely a tool to apply great pressure on Stall teams. Heatran alongside Gyarados are great stall breakers together. The latter uses Blissey as set-up bait, while the former gets rid off Gyarados's arch nemesis: Rotom-A
As far as Dragon- types go, I think Flygon and Dragonite are handled by Swampert very well, what I was worried about was taking their Dragon type attacks, Draco Meteor and Outrage which could be dangerous to handle due to the lack of a reliable resist. Heatran can take these attacks moderately well as it has naturally good defensive stats.
You also said that Snorlax is a reliable tank for this team, imo the team can run into trouble against Special Attackers late game in a weakened state. It can use the following set to fare better against Calm Mind Suicune, which can be a pain to face for this team with a weakened Snorlax on your hands:
Snorlax @ Leftovers
Ability: Thick Fat
EVs: 188 HP / 104 Def / 216 SpD
Careful nature (+SpD, -SpA)
~ Curse
~ Body Slam
~ Crunch
~ Rest
The main problem your Snorlax faces in tanking is the lack of recovery. With this set you get the recovery, while having better Special Defense to take on Suicune, Starmie, Rotom-A, etc. Snorlax still hits hard with a couple of Curses under its belt which shouldn't be too hard with Fighting types removed, and the longevity provided by Rest. Crunch is mainly for Rotom-A who would otherwise be a bit of a hassle to deal with.
Other than that, I think this team looks good, and best of luck in the future!
Sorry for the huge change in the rate, I know I suggested Gyarados/Modified Snorlax, but I forgot to take the lack of Dragon type resist into consideration.