I don't know how many NBA teams have their own little performing acts during the games or time outs, but the Indiana Pacers do.  They are known as the Power Pack. 

The Power Pack comes out at the end of the third quarter and they perform their dunks off of trampolines.  You can also catch them throwing t-shirts and other Pacer gear into the crowd during time outs.

My favorite skit they do, is when they dress up in the sumo wrestler outfits and try to shoot layups.  Boomer, the mascot, then tackles them as hard and as often as they get to their feet.  It is quite funny to watch.

I had a chance to be on the Power Pack before last season.  I trained with them the whole summer.  I will say that jumping off a trampoline and launching my body toward the basket is a little scary at first.  But, when you get the first dunk down, it is a pretty awesome feeling.  My buddy, nicknamed G-Man, is seen in the picture to my left.  He does a flip-between the legs-dunk that is pretty amazing to watch.  I don't think people realize how hard it is to do just a regular dunk off the trampoline, let alone while you are flipping and moving the ball around.  I found a couple videos of their shows on YouTube, but it is sort of far away, but you get the idea of what they do.