Are they as mean as the yellow tang? I have heard some stories that they yellow tang will pick on other fish. I have had power blue and hippo tangs and they never bothered other fish.
It really is an individual fish thing, sometimes you will get one with a nasty personality. If you introduce the tang as the last fish in the tank when all the other fish are established then it should be fine 99% of the time. Otherwise the tang usually just claims the whole tank as his own.
I just purchased a kole (yellow eye) tang yesterday. I is a little shy but has adapted quite well with my other fish. He has been swimming around with my yellow headed sleeper goby. They are pratically inseparable. I have a pair of false percs, 2 blue damsels, 1 yellow tailed damsel, the sleeper goby, and lots of soft corals. He is still very shy, but he enjoys swimming around with everyone else when we are watchign from a distance. He gets scared when there is a presence in front of the tank. I did notice that he has some HLLE on one of his sides. I'm hoping that the nice new home i gave him and a good diet could clear it up.
Purple Tang's tend to be one of the most aggressive among surgeonfish. I was hoping I might get lucky when I bought my baby PT, and after 4 years, I've not been able to keep anything with him.