Not sure for dungeons or personal loot, but I had the Survival Hunter appearance drop in our raid the other night even though our Hunters were BM/Marks. I was the only Hunter who played Survival OS and my loot spec wasn't set to Survival. So they might drop regardless of loot spec as long as you have the weapon present?
Loot spec doesn't matter, there's a lot of cases of resto/balance druids dropping the guardian hidden skin from Ursoc and trading it to their bear tank, etc.