This isn't exactly a gpm problem, but . . .

devfs overlays /dev/mouse and the initscripts and gpm rely on its
existence.  I would recommend changing the /etc/rc.d/init.d/gpm file to
directly reference the right mouse device or adding some magic to kudzu and
the initscripts to write a link at startup.  Another possibility is using
devfsd to make the links, as in:

REGISTER
misc/psaux
CFUNCTION GLOBAL symlink $devname mouse
UNREGISTER
misc/psaux
CFUNCTION GLOBAL unlink mouse

(see bug 22809 for notes on that).  However, if a new mouse is detected,
kudzu would still have to change that link somehow.  Anyway, just a heads
up on that.

This isn't high priority, since devfs isn't going to be in use anytime
soon.  I just like it when the initscripts work without kludging.