I think that Demandred was the one who helped Rand although I have no idea why he couldn't sense anything from him. I think it said that all of the forsaken have access to the true power didn't it so I guess he could have been using that. The reasons behind this are that he wants to be Nae'blis ( or however you spell it ) and i think that I read that he didn't like Sammael very much. With sammael out of the way he's the only male forsaken left (not counting the ones that have been brought back) which is a very good thing for him.