I wouldn't worry so much of inhumane treatment to get dolphins to do tricks Yankee. They are known to do the exact same tricks in the wild without coaching. It's not a far stretch to get them to do it at will. The only sad part is that they do not have the space to be free as they would in the wild.
Well, to my mind, those dolphins certainly seemed to be enjoying themselves and I imagine they have a larger area where they "live" when they're not showing their tricks .. and their training no doubt includes lots of treats