"The captured drakes in this encounter now apply Dragon's Vengeance when they are killed instead of when they are freed. To account for this change, the health and damage of the drakes has been reduced, and the damage bonus gained from Dragon's Vengeance has been increased."
From:
http://us.battle.net/wow/en/blog/2166872
Obviously, this nerfs atonement healing at the start of the fight, which could matter in heroic.
I believe the damage bonus was increased to 100% on PTR. It takes like ~1:30 min to get 2 drakes down to get to 200% damage buff? I think the spec is still good but it's probably desirable to mix in penance and other heals at the beginning.
Honestly, I am not sure though until I try it. What is your opinion on using atonement spec for Heroic Halfus?