Yes, it does, and the damage can't be reduced either. (Unlike Dark Yojimbo's Zanmato, which can indeed be reduced as The Black-caped Man claims)
Dark Yojimbo and Dark Magus Sister's overdrives have a complete Dispel, including Auto-Life. Additionally, Dark Anima's and Dark Bahamut's dispel every positive status except Auto-Life. (As far as I'm aware the others don't dispel anything, although Dark Ixion's inflicts Full Break)
As for ultimate armour... there are really two armours that I used... one for Penance, and one for everything else...
Penance: Auto-Haste, Auto-Protect, Auto-Potion, Defence+20% (Yes, the last ability works even if you already have 255 defence. Combined with 4-5 Cheers, it makes it possible to survive Immolation without Break HP Limit)
All others: Auto-Haste, Auto-Phoenix, Stoneproof, Sleepproof
Also keep in mind that except for Penance, my stats were far from maxed. The only ones that were even raised significantly were MP (500+), Strength(200+), Agility(170+) and Luck(60+).
For Penance, Luck to 85+, Defence to 255, HP to 9999 as well as MP, Strength and Agility as mentioned.
It is indeed possible to beat all bosses other than Penance (and possibly Penance himself too, not sure on that one) with these stats.