I had one that ate my zooanthids but didnt bother anything else so they are a little bit of a risk! I guess it all depends on how bad you want it and what you might be willing to risk?
Mine does not seem to bother them. He does pick at the starfish however.
-r
I must be the only person without Aiptasia. My reef is 7 years old and I've never seen one. I must have gotten lucky with my live rock.Mine never touched clams or corals but devours aiptasia!