The Copper banded butterfly(Chelmon rostratus) may eat aiptasia and may be compatable with corals,depending on the individual fish. Some of them don't touch it and do nip certain corals.
Their are many butterfiles that eat aiptasia blut most will also eat corals ravenously. The Racoon is a much better bet to eat the aiptasia than the Copperbanded but there is no question that a Racoon can not be placed on a reef since it will devastate corals. It is good in a fish only tank,however. and much better for this type of problem in this circumstance than a Copperbanded,in my opinion.