According to information on AppleInsider and their forum discussions, Nubus Macs have to boot from Mac OS 9 to install onto system.
Any system that can run 8.5 should. But clones may be an issue - unsure.
Then there are the different upgrade cards which means check with Sonnet, Newer, etc and I imagine some will need to provide driver updates.
And then FWB HDT may need to be updated if there are any changes to HD driver - in fact I have never seen a system update, even 7.5 to 7.53, that did not require such an update, or 6.05 to 6.07.
New adopters of new technology and operating systems are on the "bleeding edge" remember.