I have had a few flame angels over the years and they have all been quite different. The first one I had was a model citizen. He didn't bother any other tank mates or corals. The second one I had loved to graze on all manner of coral but was fine with his tank mates. He even lived with a potter's angel at the time (another pygmy angelfish). The current flame angel that I have now seems to be behaving himself. I have not noticed him bothering any other fish or corals in my tank.
The moral of the story is that you just never know. I personally think that their tendencies are more a personality traits rather than a species trait. Sure, angels in general like to graze and nip on polypy things (this is a known as a natural habit), but that doesn't mean all angels will do this. In captivity fish can tend to change their habits quite dramatically from their natural behaviours. Although we try to mimic their natural habitats as much as possible, the truth is we don't even come close. We expose them to fish and other critters that they would never see in the wild, or foods that they would never eat in the wild. Oops, going off on a tangent here, sorry!
Anyway, my advice is always that if you like the fish, get him. Just be prepared, and don't be surprised if things don't work out (ie, he turns into a holy terror and eats your entire collection of zoanthids
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