I think a lot depends on the individual fish you get. We just had to return our blue dolphin because he was the spaz of the tank, constantly running all of the other fish off and stressing them to no end.
I had a 5.5" male that just recently died about a month ago. I still don't know how he died. He was breathing a little heavy a couple days before he passed and then I found him floating the following day. Anyway he was a very passive fish. He seemed to always be at the top of the waterline staying away from my larger more aggressive haps. He wasn't never beat up or anything but I think could have got stressed out from all the other haps. I heard they do well in a same species tank.