Hi Gabriel,
I take it the built in Oracle support isn't working for these old versions of Oracle? (KB0019882 details onboarding Oracle DBs, but does note that Oracle 19 and 21 are the only versions tested at this time)
Looking in the Custom Platforms & Plugins forum, I see some people have provided plugin examples, although I don't think I see any specifically for databases. DavidC has posted a MariaDB Custom Platform, which is an approach you could take if you're able to manage database accounts by logging in to the database host with SSH and issuing commands from there.
If you haven't already found it, the Password Safe Resource Kit (downloadable from the portal) has basic documentation on plugin development in the "Password Safe SDK" directory.
Cheers,
Owen