Be careful with dwarf angels, some individuals will pick on coral polyps, nip at LPS and clam mantles. Not all will do it and not even every member of a specific species will do it. It pretty much depends on the individual and their diet.
It can be done, they just need to be fed well, and you need to not mind a little bit of nipping at the corals. One well fed dwarf angel, probably cant decimate a 30gal, as long as there is a lot of coral for it to choose from (spreads out the nipping).
As for my fish suggestion, Im partial to hawkfish. Just make sure he stays small enough that your other fish wont fit into his mouth (b/c if it will fit...it will end up there.) Foxface is cool too.