I have a Coral Beauty and Lattice Butterfly and they get along fine. However, depending on the dwarf angel you get, you should make sure your tank has been going for a while to give it something to craze on (my CB is non-stop in this respect). Dwarf angels do much better in a well established tank. IME, the butterfly, at least the LB I have, is a different case. First, it is not reef safe at all and ate my zoos and picked at my shrooms within hours of being introduced. Luckily it eats everything I put in the tank like a champ. I think butterflies are great - you just have to decide between them and corals. However, once you've made the choice it will open up a few doors with respect to getting some additional types [of butterflies] (assuming you have the room).