As I recall, you run like crazy during an ultimate match. Those costumes, although admittedly way cool, would seem to restrict the players after a while. Does the other team have to dress up too?
There is a certain amount of running involved, usually into walls in the indoor tournies.

You kind of move with the disc as you would in netball, i.e. not moving when you've got the frisbee in your hand, and score like in american football by catching the frisbee in the other teams endzone.
And nah, twas just us that did the dressing up in superhero costumes, and only for the one tournament. Think they managed to finish 5th in that one, out of about 14.