Most butterflies are not reef safe however, those with the longer mouths ( Chelmons, Yellow Longnose, etc) are better suited as they are more of a worm food eater than a coral feeder. So if you are planning on feather duster worms or trying to build a colony of pods
for ,say, mandarins, these would not be a good choice.
I have kept Copperbands and Longnoses by adding freshly opened Clams, Mussels, Scallops and Oysters to their diets. Plus, I made a special mixture of more finely ground foods for them which was mixed in with the "regular" food so when the other fish were aggressively feeding on the bigger chunks and getting the flies all excited to eat, they would then find the smaller pieces and would be feeding too. ( It's a little more work but the reward of a fat Copperband was worth it
Hope this helps