I thought I'd jump into this discussion, so...
Poison Heal Snorlax is... interesting to say the least. Snorlax gets the ability to not be statused(assuming it's holding a Toxic Orb and/or is already poisoned) and gets twice as much recovery than leftovers at the cost of Fire and Ice resistances in Thick Fat. Though those resistances really help Snorlax, since it doesn't have any from its typing(aside from a Ghost immunity), some passive recovery and the fact that it can't get burned after being poisoned is a pretty nice trade-off.
Snorlax benefits from this in many ways. On the offensive spectrum, it's able to fire off STAB 140 BP facades due to being poisoned, and already has a pretty nice physical movepool including Earthquake, Wild Charge, Rock Slide, Superpower, Pursuit, the Elemental Punches, Iron Head, Seed Bomb, Zen Headbutt, Crunch, Outrage and Gunk Shot. It's able to attack from a variety of types, from Electric to Steel to Poison. Not only that, Snorlax has access to Curse, which can help increase its already nifty attack stat and its "meh" defense stat. On the defensive spectrum, it's able to spread Toxic around, has the ability to phase with Whirlwind, and SubToxic stall when necessary.
However, Poison Heal doesn't help the fact that it has a lack of resistances and a weakness to Fighting, and many fighting-types can come in and take care of Snorlax with their attacks, especially since they target Snorlax's lower defense stat. Curse can help somewhat with some defense boosts, but Snorlax still suffers from lack of recovery moves outside of RestTalk(which isn't as bad as before now that sleep mechanics have been reverted to Gen 4's). Defensively, it'd have a lot of competition with Gliscor, which has access to Roost, a great defensive typing, and superior defense(although Snorlax has more HP and Sp. Def). Offensively, Snorlax would have some competition with the bulky attackers in the tier, although Poison Heal heals as much as two turns of leftovers recovery.
Some potential sets...
Snorlax @ Toxic Orb
Ability: Poison Heal
EVs: 80 HP / 176 Atk / 96 Def / 156 SpD
Adamant Nature
- Curse
- Fire Punch
- Facade
- Earthquake
This is Snorlax's good ol' Offensive Curse set. After a single curse, Snorlax is able to plow through some of OUs prominent threats, OHKOing Talonflame, Mega-zard Y, the Latis, and can pull a 2HKO on tank-zard X without rocks, and 2HKOs Chansey with just Facade. Earthquake pulls a KO on any Heatran after +1, and can help nail Lucario and Terrakion. Crunch doesn't get many KOs that Facade doesn't nab, but it helps nail Ghost-types and Bronzong. Other options include Fire Punch to nail Ferrothorn(2HKOs at +1), Scizor, and Mega Scizor(unless it's running max Defense and max HP, which is OHKOed at +2). This thing severely damages most of the metagame. It's possible to run Crunch in place of Fire Punch, but eventually Fire Punch will hit Ghosts hard enough.
This set has a few issues. Lack of reliable recovery outside of Poison Heal can hurt it, and it has a bit of a 4MSS. Without Crunch, it misses out on some KOs on Ghost-types, and without Fire Punch, it misses out on KOs of Ferrothorn, Skarmory, and Scizor. Something random that just came to mind is that Cofagrigus(lol) can get rid of Snorlax's Poison Heal with Mummy, and since the toxic is still technically racking up even while it has poison heal, the Toxic can come back to bite it. Also, if the opponent manages to burn Snorlax before the Toxic Orb activates, it's pretty much dead weight. Snorlax might also have some trouble coming in, with a lack of resistances and a weakness to fighting.
Most of what I wanted to say has already been stated, but...
Poison Heal Snorlax would need something that can counter(or at least check) Cofagrigus for reasons said above. Hard hitting special attackers can do the trick, such as Keldeo, which can 2HKO with Hydro Pump in the rain if scarfed and has a chance OHKO with Hydro Pump in rain if specs, or always 2HKO outside of rain if specs. Trick Room could really help Snorlax, but after a curse, it only has 3 turns to abuse it, although that's enough to pull at least one KO on something.