References, yes. Same characters? no. Its a different universe from FF. The characters act like they did in FF, but things that happened in the game didn't all hapen to them in KH (like said before, just look at Aeris).

That's not to say that some of the things that happened to them in FF didn't happen to them in KH. It could have, for all we know. The FF characters are just there to spice up the game (If not attract some FF players) and thus are not too insanely important.