I have a 30 gallon biocube with a pygmy cherub angel (centropygae argi) who shares the tank with a pair of ocellaris clowns and a yellow watchman goby (my avatar). I remember being told that my tank wasn't large enough for him (not by anyone here though, I think) but it seems like he's got plenty of space. I love the little guy, he is tiny but a real stunner, especially when he catches the light just right. I have caught him nipping lightly at one of my leathers and a couple of zoanthids a few times, but the corals don't show any signs of distress so I'm not particularly concerned. Anyway, you've had one yourself so you probably know all this already
I originally wanted a flame angel but decided my tank wasn't quite big enough. Perhaps if the angel was very small and there weren't any other fish in there, but I would still worry about swimming room. Of course, I am by no means an expert so maybe it would work well. If you do get one, please, post about it! I couldn't find any accounts of someone trying to keep one in a tank that size when I was researching my options.