There are many excellent arguements that Taim is Demandred, enough so that I am fairly convinced this is true. Two last arguments apply: 1) Demandred is present in Caemlyn T'a'R observing Nynaeve and Elayne in LoC. same time line as Taim residing near Caemlyn.
The second is more complicated, and involves Sammael and Lanfear Recall that Rand was being directed toward a confrontation with Sammael long before CoS came into play. Also recall Lanfear stating that Rand was being led to believe Sammael was behind many attacks against Rand. Thirdly, recall in LoC that Sammael believes Rand accepts an offer of truce (he says this directly to Graendal) yet there is still an attack against Rand by a gray man, where Taim coincidentally shows up to save the day and kill the gray man before the CAPTURED gray man can talk (can they talk?). Taim then offers the excuse that he found a man with the spark inborn coming to tell Rand in direct disobedience of Rands orders for ALL Black Tower initiates to avoid Caemlyn. I believe the gray man was sent by Demandred to make Rand believe Sammael is on the offensive. I also believe that if Taim is not Demandred, T at least works for D.