I still don't have the R80 working, but I do have a UDA50 and a RA81 with no HDA. I hope to get an RA90 shortly. I have booted BSD unix with 3mb of memory and a miniroot on an RL02. To do it I had to hack a version of the NetBSD 'boot' to run on the 730. I added a 'copy' command which allowed me to copy the BSD miniroot to a tape. I then booted the stock BSD copy program and copied the tape to the RL02.
NetBSD doesn't support the 730 (yet - I'm close to fixing that) and it's boot program knows nothing about the "IDC" or RB730 controller.
BSD supports the 730 and has a driver for the IDC/RB730. But it's boot program does not support any network cards (i.e. DELUA).
Hence the hybrid strategy...