I've had flame angels over the years in my mixed reef tanks and never had a problem with them.
I know that they nip at many things and as long as they move on and don't come back to the same spot nothing is harmed.
I just had to euthanize my flame that I've had 8-9 years. It never bothered softies or lps.
I probably wouldn't trust any with clams.
In the process of taking my old leaking tank down and moving the fish to a smaller temporary tank one of his eyes was damaged.
Within a day the other fish attacked it and he lost the eye and part of his forehead.
I actually just took my Flame out yesterday....he is sadly going back to the fish store. He was fine for several months than started nipping my Trachyphyllia. It got to the point where it wouldn't even open anymore. I have had 4 different species of dwarf angels and that is the only one that has caused me any issues.