My starry rabbitfish (Siganus stellatus) loves zoas, clams and GSP. It doesn't seem to touch shrooms or anemones. I will caution that it likes to taste new growth on SPS. It can be a hassle if you've got a few frags like me, but I doubt you'd notice much in a mature reef.
It seems to be a pretty timid fish and I didn't see it much until I put a blue throat trigger in the tank. I don't know if it's because I only had four fish and they all hid whenever there was motion outside the tank, but it's out almost constantly now with the trigger and 9 fish. Mine went from about 3" to about 7" from May to now, so almost 1/2" of growth per month.