Yes you can make DoD maps with Hammer.
You just need to create a DoD game config in Hammer with the dod.fgd (google it?)
You need GCFScape:
http://nemesis.thewavelength.net/index.php?c=76
to get the DoD .WADs from Steam's cache files which are in your SteamApps folder.
I've never made a map for DoD so that's about all I know.