Theoretically, Desktop Redirector would only be used by a device that's not connected to BES...right? Otherwise, what's the use for it if the user is already synching via BES?
That said, it would make sense that you couldn't disable the Desktop Redirector from BES since 99% of the time a user wanting to use it wouldn't even be connected to BES and thus couldn't receive a policy setting disabling it.
Am I misreading your question?