I would have to say that although i have got this stuff all working with Oracle now - reliance on JPA and persistence units for the database creation is just a hideous nightmare.
The fact that you have to trawl into various jar files to modify persistence.xml files and mappings if your database platform varies from the provided h2 database is a real headache. Even just changing the database host for different environments is non-trivial - particularly if you want your application and the JBPM toolset to point to a persistent database.
If you are planning on using Maven for your build process, and plan on running jbpm inside a container, be prepared for significant packaging issues!
The provided hibernate mappings are not compatible with Hibernate 4 and Oracle. The Maven dependencies for 5.2.0.Final are not compatible with JBoss AS7. Virtually every step of what should have been a simple process has been time consuming and frustrating.
If you are looking for an 'install and use' component in your system to provide BPMN workflow capability - i definitely wouldn't recommend JBPM5 at this stage. I would be looking at Bonita or something more mature.
Unfortunately, we had this part of the technology dictated to us for a proof-of-concept. I will certainly have a reasonable amount to say in the lessons learned phase of the POC.
I also wonder what the upgrade path is going to be for these components? If DDL was provided, at least you could assess if there were any structural changes - and plan data migrations to the new strucutre. As far as I can tell, the process currently would be to run the jbpm componets with hibernate auto create set to 'create' or 'update', assess if the resulting schema differs from the previous one - and then worry about how you get your data from the old one to the new one.