@Andrew respectfully, 7.5 has the same issue as does 7.4. As well Xcp-ng 8.2 worked perfectly fine for the Xen PV devices. Totally reproducible.
- Install Xcp-ng 8.2
- Setup/import OpenBSD VM.
- Boot and see xnf devices just fine.
- Upgrade to Xcp-ng 8.3
- Boot the same VM and see the xnf devices show up as re devices (realtek driver) and watch interface give re0: watchdog timeouts during an install but if VM already built you'll be able to see the re# devices but can't assign addresses to them.
The difference appears to be the xen version difference between 8.2 and 8.3.