jBPM5 uses JPA (with Hibernate as default persistence provider) to persist process runtime data. The tests use H2 in memory database simply because it is easy to set up and test. But the persistence configuration can be updated to a lot of different databases. I've just updated the documentation (it should show up in a few hours on the URL you mention) with a separate chapter on persistence, and that contains some information. In general, you should just update your persistence.xml and the datasource you are using.
If you still have questions after reading the updated documentation, or problems when changing the configuration, just let me know.
It would be great if you could also document what changes you are making exactly to get it to run on oracle, as we could then extend the documentation with information like this ;)