No butterfly is guaranteed reef safe. Copperbands are definitely one of the safer bets, but do carry the chance of nipping coral polyps. They do also come with the baggage of being more delicate as they are less likely to take to prepared food in captivity. Pyramid and kliens are also pretty good bets but again it's on an individual basis.
It should also be noted that a "model citizen" can turn. I had a friend lose thousands of dollars of acans in a 24 hour period to a regal angel that had been living in the tank for years. She's not sure what happened - maybe it picked some food off of a polyp, got a taste of acan and decided these were too good to pass up.