I have a flame, halfblack and bicolor in a 200g. They all get along pretty well and have lots of space. I have zooanthids, mushrooms and Lps and after about 6 months I have yet to see them nip at the corals. The halfblack nipped the clams to death however
Im pretty sure clam mantle mucus is like crack to dwarf angels!
Anyway I agree a bicolor is too large for a 30g. Like everyone is saying your always taking a chance with any dwarf angel in a reef. You can try a flame just make sure to keep it well fed. Give it nori seaweed tied to a piece of live rock to munch on instead of your corals. And definately the smaller the better. What about the cherub angel that some people have mentioned?