That's part of Vincent. He wears that claw in FFVII. Then there's the bandages around Cloud's Braver. Those weren't there before, nor were they any part of Vincent. There were those mummy things outside of where Vincent's coffin was (random battles), but that makes even less sense. I'll just go with "it makes him look cool" for now, I guess .
I think it'd be kinda' nice if Zack made a appearance in KHII also, but he probably won't.