John
I guess I'll be the counterpoint to thread so far. As others have said, no angel is to be considered safe around any corals. I, too, had a coral beauty that was a model citizen for well over a year, and then took a liking to the open brain. Killed it. Never bothered anything else, although he did take one or two nips at the E. ancora. Each fish is an individual, such that any advice you get about a species' behavior needs to be taken with a grain of salt. Nipping corals is what Centropyge do in the wild, so anytime they're placed in proximity to coral the possibility exists, even after long periods of time. You pays your money and you takes your chances. If you put a pygmy in, just be ready to pull it out one day in case it begins to be a problem. If it's healthy your LFS should buy it back. Don't blame you for considering getting one though - they're beautiful, active specimens. I guess the bottom line is that I would recommend against it. But if you go ahead, never let your guard down with it, and have contingency plans ready for removal. Best of luck with your decision.
-rw