If they brought a live Dolphin back, I'm sure PETA would have a word or two to say about it. Support them or hate them, I would have to agree with them in this case if they did object. Here in Colroado I see the Bronco, a Buffalo and a Falcon (Air Force) all used but there isn't really much stress, I wouldn't think, to present those animals. A Dolphin??? That's a whole other story.
Which begs the question...why doesn't San Diego use a giant Tesla Coil, or something, in the middle of the feild to generate some lightning bolts!?!? Imagine night games! Light up the stadium, strike a few fans...now THAT would be cool! Or the Miami Heat can fling flaming baskeballs into the stands! Sweeet!
Edit: In all seriousness, I think it would be cool to have a sort of mini-aquarium at the stadium with a handful of dolphins. Maybe borrow them from the Miami Seaquarium for the season and return them in the off-season.