Oh, probably...
And now that my seahare has "discovered" nori,
now he doesn't seem to touch anything else either!
Anyhow, I don't know about the powder browns (or any
Acanthurus sp. tang for that matter), but basically, I've never had a
Zebrasoma sp. tang that was the "answer" to any hair algae or other nuisance algae (including caulerpa, which was never touched .. I had actually purchased the Red-Sea sailfin to help deal with unwanted caulerpa). If you have one that does graze the stuff down, treat it as a happy bonus; but probably best to not count on it.