The short answer is that NetBSD/pmax won't work on a mips workstation.
For starters, most (if not all) mips workstations are big-endian,
whereas the pmax is little-endian.   If that wasn't enough, the I/O in
most MIPS workstations is different than that in the various DEC
workstations.

Tracking down the documentation is probably the right thing to do - it
may be possible to do a port pretty easily if MIPS used similar I/O
devices.   I can't help you with that, but maybe somebody who's
lurking on port-pmax can...

			       _MelloN_