Well, if he doesn't help, Orochimaru isn't going to keep him around.

Orochimaru has said before, that he doesn't know what he's thinking or something along those lines.
Wouldn't suprise me if Orochimaru knew who the spy was, and was using him to his advantage, with knowing where the Akatsuki are, or wher some members are.
Could be a reason why the Akatsuki, can't get their hands on him.