There is a bit of confusion over how the Raid Finder interacts with the Saga of Zath quest. I’d like to clear this up:
Boss Kills in the Raid Finder will NOT update your Saga of Zath Quest. Players must defeat the bosses in organic raids in order to receive credit for their Saga quest. I’ve added this information to our FAQ.
I’m very sorry that the Saga of Zath Quest is not clear in this regard. We are investigating elegant ways to make this more clear.