My flame picked at my clam alot for the first week. When I say alot, I mean about every 10 mins. After that first week I've never seen him pick at it again.
Now I only see him pick at the live rock (keeping my fingers crossed).
He doesn't mess with my blenny or 6 line wrasse. But, I was holding a purple tang for my friend for a few weeks. The purple tang would try and pick a fight with the flame and the flame would ignore him most of the time. Expect every now and then he would get sick of it and fight back, then the purple tang would run away.