This is mostly because of their terms and policies regarding retracking existing accounts. Even though you haven't deposited any money, you still have an account which is tracked directly to them, and there's close to impossible to talk full tilt into doing it.

Other sites might not be as strict about it, but I recommend mailing our support before you make the deposit, so that we can contact the site and get a clear answer if they retrack you and add rakeback trough us or not.

Edit: Sorry for this very late answer, I have no idea how I could over look this thread.