Linux is GPL. I've yet to see a DRM license that is compatible with a GPL embedded system, or even LGPL in most cases (because of the reverse engineering clause).

Hackability is less of an issue in that the firmware and OS would have to be encrypted in all cases, but my point there is that a closed encrypted Linux distribution is no more useful to the owner than a proprietary OS. Having the source doesn't help if you can't upload modifications (is that even allowed by the GPL?).

Rob