I have a regal and PBT as well. The regal is king of the tank and I would have thought there would be some aggression upon adding the PBT, however it wasn't from the regal. My scopas (thougth was the most mellow fish ever!) was checking out the PBT and bugged him for about 2 weeks. I have lots of hidey holes and spot fed the PBT (fed the fish at one end of the tank and the PBT at the other). They're all fine now, sometimes there is some tail flashing back and forth between the two but other than that no problems.
As for their survival rate, no its not the best. I think they're ich magnets. Knock on wood I've never had any ich on mine, but I did have a neon goby in the tank at all times and he did a great job of keeping them all clean. Best you can do is get a healthy looking one that is eating at the LFS. I was pretty leery of trying one of these fish but happily I've had him for almost 2 years now
