Kemtrossaid: I get the theory that it's Oreb, but I'm not sure about it. Mod Raven did say that they wouldn't be introducing a new character just to be Sliske's master, and I think that would include Oreb.
But that's the thing. Oreb wasn't introduced just to be "Sliske's" Master, was he? He was Nomads first and we had our first "Proper" introduction to him as a character as Nomads master, well technically planting the memories for us to find, but semantics.