Hmm...
Arcanine has little going for him aside from being one of the bulkiest fire types possible (lol), so maybe some UU testing for him. Claydol is a nice spinner, but I don't see him sweeping nor walling entire UU teams. He'll be bulky of course. Drapion seems interesting as a UU wall also, certainly stoppable with the earthquake disadvantage, but nice resists and stats may be too much...
Houndoom is a glass cannon, weaker than Weavile in both defenses, and only 110 Sp. Atk to cover himself. But he seems too strong for UU, but I'd be willing to test him if anyone else is.
Ninjask can be phazed, and I don't see him sweeping teams. Roar Walrein pwns him already, and probably Noctowl / any whirlwinder as well. Stealth rocks hurt him a lot this generation, so I'd be willing to test.
I'm also willing to test Shedinja, simply because stealth rocks / spikes kills it completely.
Heh, some of the guys I'm looking at seem a bit powerful >_>
Base power easily makes up for Houndoom's lower primary attacking stat. Weavile's Ice Punch is only 112.5 power after STAB, whereas Houndoom's Flamethrower is 142.5, Fire Blast 180, and Overheat 210, combined tby the fact Houndoom can get a further boost if it switches into a Will-O-Wisp or other fire move. Furthermore, Houndoom easily destroys most of its would-be counters with a Super-effective HP after it gets off a Nasty Plot, whereas even Swords Danced Weavile's Ice Punch still couldn't take out Hippowdon or Rhyperior. Houndoom also has the option of going mixed with 90 Attack (compared to LOL 35 SA Weavile), and as crappy as Fire is defensively, Ice is worse, and Houndoom has 2 immunities to work with and more resistances. Houndoom also has ways to wipe out its would-be counters, whereas if Swampert or Skarmory switches into Weavile it pretty much has to run or be slaughtered/set up on. Weavile's defenses are also only marginally better than Houndoom's. 70/65/85 vs. 75/50/80. Since the idea behind both of them is you'll never be taking a physical hit, they work about the same way.
If allowed in UU, Houndoom would also have the devastating option of Nasty Plot + Powerful Herb Solarbeam, which would quickly silence any water type switchin and leave Houndoom open to sweep, especially if it came in with Flash Fire activated. HP Water, and Dark Pulse would round out its compliment and ensure no fire types came in to ruin its day either.
I wouldn't discount Arcanine. It has great mixed attacking potential, an 80 power no drawback priority move off 110 Base attack, its Flare Blitz is obscenely powerful, and it gained physical Crunch and now has Reversal to play with. Since Stealth Rock deals 25%, Arcy can still Subversal just fine if it's out. It even has Will-O-Wisp and Thunder Fang if you're so inclined. Remember, this has the highest non-ledendary non-600 club stat total in the game, and both of its abilities work very well.
Remember what people say about Entei: It's a bad Arcanine.