I can't say for certain, but I don't know of anything it won't eat other than soft coral tissue. When I hang Nori for my tang and lawnmower blenny, he often makes a beeline for it. I'm not sure how much the tang or blenny get.
I know it eats hair algae and coralline algae and sometimes nips sps corals if they're small enough frags that they don't present a large enough profile to prevent it. I know I did have some valonia (bubble algae) in the tank for a while, and I just checked and couldn't see any. I don't think anyone else in there eats it.
I think if its mouth can get close to it and it's hard or smells like algae, it will eat it. It leaves LPS and softies alone as far as I can tell.
It's an interesting creature (it is everyone's favorite spectacle in the tank, but it's not compatible with some of my future species so at some point I want to trade it out if I can, or just drop it in a refugium).
Brad