I am currently on the great hunt on my second run through the series, and a thought occurred to me. The a'dam allows sul'dam to control aes sedai, which often involves using the power as a weapon. However, as I remember, the oath rod makes the oathes binding to the point at which the aes sedai who swears them is physically unable to break them. That being said, it would seem that this inabilty to break the oath not to use the power as a weapon would still be in place on the damane. The only explanation I can come up with are that with the sul'dam controlling the aes sedai, it somehow counts as using it to protect ones life. However, it's been a while since I've read these so I can't remember exactly how the sul'dam channels through the damane or if she is merely controlling her channeling.