In the 3.7.3 QuickStart section in the user guide there are steps for configuring jbpm to use a different database which I have followed for setting up an Oracle DB. In addition to what's mentioned in the user guide, I found another persistence.xml file that looks like it is used in the jbpm-human-task-war.war file that is located in the \task-service\resources\war folder. I believe this also needs to be updated and should be added to the documentation.
The other thing I think would be useful to mention is the repository.xml file which is used for the guvnor repository. Although the drools-guvnor web-app can be used to create a new repository.xml that can be used it would be nice if there was a short procedure on how to change it along with which folders if any can be removed after changing the repository to use a different DB.
Cheers,
Jim