i think some of the alternate costumes could possibly be other characters...but only certain ones, such as cloud and zack, or bartz and his alternates, however, i highly doubt that one of terra's alternate costumes is locke it's a completely different gender!

also, with the onion knight 'confirmations', they're not alternate cosutumes, and it's not Luneth, either, it LOOKS like luneth because it's the same class, but that form and another mage form (sage?) are part of the OK Ex thingy...i forget what it's called, but the overdrive...so i don't think that should be counted

EDIT: Amarant sucks, if there is an alternate character for Zidane, i hope to God it's not him....i want Vivi in this game, but he's hardly an appropriate costume change for Zidane