I agree, I think that's the only thing he was really worried about. And he probably only wants to use this "alliance", or whatever you want to call it, with Sloane so he can learn more about Rambaldi and so he won't have to run into him trying to get all of Rambaldi's works. I think later on Sark may break off and betray Sloane. However, he did seem the type to take orders in a few episodes.