The AI merchants apparently have no FOW, they are rapacious, and they usually have incredibly high levels early in the game. I have begun to use them to train my assassins. The fort exploit is no longer available in Kingdoms but you can still put military unit on the resource and load it up with merchants (it is safer to use a trustworthy general). I am beginning to believe that recruiting merchants are a waste of money until turn 50 or more. It seems that I can blitz significantly faster without building them or many other agents.