The disk is set up with an HFS (not +) partition at the beginning of the disk with ofwboot.xcf, netbsd-INSTALL.gz, and netbsd copied to it. netbsd-INSTALL.gz booted fine, netbsd didn't, then when I gzipped netbsd and copied it there, that booted. This is a Mac mini G4, BTW.
OFW in Mini G4 groks FAT and I've been using FAT partition for boot (just the ofwboot*, the kernels are in the netbsd root fs) for ages now. Plain MBR, no apple partition map. /boot can be mounted natively.
ofwboot.* can load netbsd from FFS? How did I miss this? Granted, it's been a good twenty years since I was burning kernels on CDs to get NetBSD running on a G3, but if I had known...
I think my habit of using HFS is in part because I've shared disks between OF 1.x and OF 3.x systems, but good to know in the future.
Now that I think about it, I've long forgotten the difference between ofwboot.elf and ofwboot.xcf. I suppose it's not hard at all to copy ofwboot.elf and try it out.
Thanks! John