Hi Stephen. I don't know about the user profile manager. But for 5.2, you have an interface called org.jbpm.task.service.UserGroupCallback. When an operation to task server is done it will check in the defined implementation whether the user or grupo exists, and get the users of the groups.
You can write an implementation of this simple interface, and set the system property jbpm.usergroup.callback with the name of your class (or user a .properties file), and then you will have the integration between your enterprise security framework and jbpm6.
Hope this helps,
Demian