A. MDOP is a per-device, per-year subscription that's available for computers covered by an enterprise agreement. It gives those devices access to all the parts of MDOP, including DaRT and its updated versions of many of the tools Microsoft acquired during the Winternals acquisition.
Because MDOP is licensed for desktops, does that mean you can't use it on your servers? If every desktop in your organization is covered by MDOP, you're allowed to use DaRT on your servers as well, but every desktop must have MDOP. There's no other way to get DaRT licensed for your servers.