Ashes of Outland Cards List & Guide
Are the new adventure cards draftable in arena as well?
I am not aware of any change to the Arena rotation list, so my guess would be no.
This set would not count as part of Descent of Dragons. It would be listed separately as Galakrond's Awakening.
(Also, I can't imagine they would add a partial set under the current rotation system. It will be several weeks before GA is fully released.)
Complaining about RNG in Hearthstone won't convince anyone that it's a bad thing -- it only makes them think you're too dimwitted to find a game that suits you better.
Yes, they are. I was surprised. My last two decks contained Frenzied Felwing.
Edit: I've also seen Hailbringer played, and I've been offered Boompistol Bully in a draft.