I'm assuming it'll only proc when you cast it. No idea if the Creepers themselves can benefit from it.
Limited testing shows a proc on creeper cast, and none after.
The buff does affect the DOM. (~21% dmg increase)
It will definitely only buff you once, when you activate the Carrion Creepers power.
I believe that the creeper patch itself may be able to benefit from the damage buff when it procs, but I think it will only proc off the immobilize, and won't affect any vines that have already been summoned, so in general I'd say "not much".
I wonder if the proc might be firing for the Creepers themselves. That wouldn't be terrible useful, but still worthy of knowing.
So I stuck the Ascendency of the Dominator: Recharge/Chance for +DMG proc into Creepers, in place of a recharge IO.
Anyone have any idea how it will work there?
Does the Chance for +DMG only proc off attacks, or is it x/times per minute as long as it is slotted in SOMETHING.
Thx