The game just popped up on Green Man Gaming with 15% discount ($42.45 USD) and it has a tag "Cannot be traded in" which is a strong suggestion that it's gonna be a Steamworks title. Not certain but very likely.
EDIT:
Just ran a search on the forums and of the moderators had this to say:
GMG Twitter Quote: Our version is a Capsule title that will be using Securom, sorry. /Rob
For the record - if it's going to be Capsule version of SecuROM DRM it will not have the activation limit standard SecuROM does (like the one featured in Arkham Asylum).
EDIT 2:
Forgot to mention, they have a 20% off coupon HAPPY-PAYDA-YSITE which can be stacked with the 15% pre-order discount, bringing
Arkham City down to a very tantalizing $33.96 USD!