I was looking through the MESS drivers to find one that uses the same graphics chip (the NEC µPD7220) as the NCR DMV and already has the UPD7220_DISPLAY_PIXELS_MEMBER entry populated.
The Epson QX10 driver fits that category, and it seems to use a similar model to differentiate between its monochrome and colour graphics adapter (1 colour plane vs. 3 colour planes, on the DMV 32KB vs. 96KB of graphics memory).
Unfortunately the QX10 driver still seems to have some issues as the one disk image that boots into a graphics mode automatically (the keyboard's dead too) has the graphics sort of backwards.
The disk image in question is mathprof from Don Maslin's disk archive and can be found here http://fjkraan.home.xs4all.nl/comp/qx10/disklibrary.html
The missing graphics mode prevents a number of software items from running on the DMV driver, such as the DMV graphics demo that can be seen here http://www.youtube.com/watch?v=7Q49hD1gci8
The program should be demo5.com that can be found here https://dl.dropboxusercontent.com/u/55419307/80NCRGRF.TD0