I always read Taims 'dark aura' and all of that as a strong hint that he is a powerful darkfriend, nothing more.

I also think the TP is restricted to the Nae'Blis. As a consequence I think the DO is setting up Rand to take that place and that is why he let him use it (but my guess is that this link will also be important for destroying the DO).

I think Taim has a different part to play, I imagine he might become one of the new generation of forsaken (since Rand is balefiring all the forsaken, there is room for new ones).