With his choice of colors in the black tower, i think its more likely that he is working under Moridin. Also, Taim and Demandred gave the same orders, to the same person in WH, why would Demandred feel the need to tell Taim's cronies his orders directly, especially if he had already commanded Taim to tell them. It seems to me more likely that Demandred was Co-Opting the Asha'man from another forsaken, weather it was Moridin(more likely) or Osan'agar (sp?) is still up for debate in my mind.

Was the Reborn forsaken playing a similar role to his twin dagger, or was he playing a more active role. Like his counter part in the white tower, tunning the black towers version of the BA. I think that until Rand took him at his side, he was basically calling the shots at the black tower, working directly under Moridin's control to be sure.