OK.  This should probably be in the FAQ...

As far as I can tell, the OF drivers for the internal SCSI bus
(MESH) do not work with my G3 card installed.  The drivers for the
external SCSI bus (53c94) do work, however.  I'm now booting
NetBSD-1.5_BETA with the 1.4.2 boot blocks off of my external hard
drive.

Hmmm...  One other difference is that I've got SCSI ID 0 on the
external and SCSI ID 1 on the internal.  I wonder if that makes
any difference...  I can't see how, though, and I can't check that
out very easily any more.

-allen