You can see Gogo and Umaro in the ending, but only if you got them during the game. Gogo mimics Celes so he/she can stop over a swich in the floor, and Umaro... Well, I can't remember what Umarop did, but I remember him doing something in the ending.

And it doesn't matter if Clyde (the person behind the cool ninja outfit) got out of Kefka's Tower, or stayed behind and died when the tower collapsed. Shadow died in that place.