I read your title I thought "wow! that must be one hell of an aiptasia! isn't it usually the other way round?"
Ok, joking aside, it's almost, but not quite 'hit or miss' when it comes to butterflies.
In my experience Raccoons are a decent bet with long nose & some heniochus other safe bets, but generally, the more 'reef safe' the butterfly fish are said to be, the less chance that they'll quickly & effectively tackle your aiptasia problems.
I've kept Raccoons, Various Heniochus, Raffesi, Auriga, Red Tail, Chevron and various Saddlebacks all in reef environments and they've pretty much all eaten aitasia/majano without harming my clams or mini-maxi's. Like Tony says, this is probably due to lack of protuding dangly bits.
The degree of 'reef safe' the butterfy you choose could potentially be directly related to just how badly or quickly you want your aiptasia gone and how much you're willing to risk the other stuff in your tank in the process.
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