In other wors grasping at straws to fit some crazy notion that everyone has to be someone else, which is characteristic of all the "evidence" for the R=U theory. Ultimecia is just Ultimecia no one elsem. Just because she isn't superdeveloped and comes into the plot late doesn't mean she has to be someone else from the game. Where did these crazy ideas start springing up? No one ever said Zemus must be Edward after he came back from hiding just because he shows up so late in the game.