I have given up trying to boot off the OS X server and now have my NeXT 
booting off a NetBSD/i386 box.

Here is what I get from the slab:

Requesting BOOTP information... [OK]
Booting /boot from
.............................................
 >> NetBSD BOOT [$Revision: 1.2 $ #3]
net_open: netif_open() succeeded
net_open: NFS mount error=-1
en(0,0,0): -1 = Unknown error: code -1
load of en()netbsd: Unknown error : code -1


But, if I boot the slab to NEXTSTEP I can mount the client filesystem 
normally.

A couple of people have noted that NeXTs have trouble with crossover 
cable, but I don't have a hub to check if that's the problem here, 
unfortunately. Any other ideas?

Thanks,

Aram