I don't mean ooc as bad fanfic, but rather, "ooc" as a personality different enough to mark an entirely different person, to the point of original character.
Like Adam said, do you think of them as the source characters? Do they have the speech patterns, the mannerisms, the thought process of the source characters, their background history and motivations? If so, you're still doing fanfic. Even if it is a whole original universe and a xover AU.
And again, think of the audience. A general audience won't notice these features, but a fandom audience is likely to recognise characters based on these features even with another name.
Ultimately, I think it matters less, if you're not going for publishing. If it's well-written and the characters are round and mesh well together, it doesn't matter. Maybe warn readers that some of your characters are loosely based on or derivative.