I don't know what I think about all these theories, but I don't think that the ghostbloods are bad guys. For one, they seem to be asking shallan only to do things that team radiant would want to happen anyway (besides recruiting an unmade for them) and if kelsier would join them, their goals can't be to nefarious, can they?
I definitely agree that they wouldn't get along with Hoid, though. He really needs to get some better allies.