As I had a very small window to do this job, I ended up using 5.9.0 to try out my proof of concept. OpenACS 5.9.1 seems to have some changes to ACS_REL_TYPES that would require more time to make the Oracle changes than I have available at the moment (but I will get to it once we proceed with this project).
The good news is that I managed to get OpenACS 5.9.0 up and running with Oracle 12c on Windows 2012 and using Maurizio's version of Naviserver. I had to fix a few things and also noticed some issues, all of which I will post on the bug tracker.
Good job all around, and looking forward to further developments with the community!
Brian