No butterflies, almost all are predatory on reefs. The safest one is the Auriga Butterfly but that is still risky. What size tank are we talking about? A pygmy Angel (Centropyge) should be fine. Anyway, hope this helps.
Our research showed that a tibeken angel (keyhole) was reef safe. We have one in our beginning reef and so far so good. We provide Nori sheets and romaine lettuce daily that seems to keep him busy. We have sea mats and a mushroom so far. We are at about two months and keeping our fingers crossed,