I've never found Roar to be all that useful, I'd probably just mention it in the moves section at best. Out of the examples you provided, the only thing that Chesnaught has any business forcing out with Roar is Garchomp. Roar does nothing to Gengar, and in all honesty, you probably shouldn't even be staying in on it (unless under a very special circumstance) due to the fact that many Gengar carry WoW. Swords Dance Aegi is better checked by Quag or Skarmory and why would you even try and stay in on Mega Pinsir is beyond me. lol There really aren't that many set up sweepers that Chesnaught can force out without either being KOed or being seriously crippled in the process, which makes Roar a very poor option in that sense.
I do see the whole shuffling appeal in the second set, but Defog pretty much kills this strategy, as every Defog user doesn't really care much about what Chesnaught can do and most can put a serious pounding on it. I don't see the point in a set dedicated to shuffling with hazards when every defog user shits on you, the way Chesnaught should be setting up Spikes is when it forces a switch; in other words, you should only set up Spikes when its convenient, not direct its entire role towards doing so.
This replay in a smogon tour match sorta demonstrates how its done:
http://replay.pokemonshowdown.com/smogtours-ou-2933
There's a reason why very few Pokemon dedicate sets towards setting up Spikes, and I don't understand what makes Chesnaught any different to the point where it deserves a set for such a role even when it's at a natural disadvantage when up against a vast majority of Defog user.
I'm not sure if there's any point in having two different sets. Imo, they should just be merged and it should look something like this:
move 1: Spiky Shield
move 2: Leech Seed
move 3: Hammer Arm
move 4: Spikes / Synthesis
ability: Bulletproof
item: Leftovers
evs: 252 HP / 252 Def / 4 SpD
nature: Impish
In regards to the Spikes / Synthesis slash, it's really all about a matter of preference. Between Leech Seed + leftovers, Chesnaught isn't all that reliant on recovery to stay healthy. So for that reason, I don't really believe it is required, but hey, reliable recovery is reliable recovery and is damn good to have. However, I did find Spikes to be the best filler move out of the two, the reason being is that Chesnaught is capable of forcing a lot of switches; as a result, it can capitalize on that by setting up a layer of Spikes that very turn. This works so well in wearing down the opposing team and makes Chesnaught all the move annoying.
As far as the team options are concerned, I think SpD Talonflame is something good to mention here. SpD Talonflame completely walls Zard-Y and can switch into Fairys rather easily on top of being able to handle Mega Venusaur and Deo-S, all Pokemon that Chesnaught struggles with. In return, Chesnaught can easily take down Ttar and somewhat deal with Rotom-W. The combination is just so gorgeous and plays out really well in practice. You mostly mention offensive partners, but I find the lack of defensive partners to be disappointing. Basically, here's a few defensive Pokemon that pair pretty well with Chesnaught: Quagsire, Zapdos, and Skarmory. What you have now is okay, but I think mentioning a little more is nice. These Pokemon also deal with set up sweepers just fine via phasing of their own or Unaware, so it really lessens the need towards using Roar on Chesnaught
, Chesnaught becomes able to take on things like Choice Specs Keldeo as long as rain isn't present, to give an example of its special bulk. The calcs all show the most powerful moves that pokemon can use against Chesnaught:
