Flame angels can be quite beligerent. About a decade ago I had one in a 180 along with a yellow tang, a clarkii clown, and a few small gobies etc. The flame would constantly "pick a fight" with the clarkii - the latter was happy to live in peace, hosting in a sacrophyton coral.... but every time the flame would swim past it would make a move. As such, it was not "serious" (so I thought) ..... no real damage was done..... until the clarkii sustainaed an injured eye, which ultimately led to its death.
I have had a couple of other flame angels since then, which have been far more mellow. But I would be very cautious mixing a flame with a rusty which is very similar is size, colour, and shape.