It was my understanding that the mindtrap is used to keep tabs on, and direct the actions of, whomever you have gained control over. Cyndane and Moghedien are already agents of the Shadow, but being mindtrapped by Moridin has severly curtailed their independence. This does not stop them from wishing and desiring to do their own thing. Witness Mogy's balefiring of Nynaeve's boat in the harbor. Strictly her own action, not Moridin's. Thus, I am forced to assume that anyone NOT a Darkfriend who would be mindtrapped would be forced to obey the commands given by their captor, but would not necessarily be turned to the Shadow, as they retain their own desires and wishes.

Forgive me if I'm wrong here. But this was how I'd always understood the situation.