Is it possible to use mixed persistence providers? I am planning on using jBPM which uses hibernate mapping files along with the sessionFactory. I am going to use JPA with EJB 3.0 to model my business objects as entity beans and so I need to use the entityManagerFactory also.

There is no rule that says an application can't mix and match both.

Be careful of classloader conflicts, and potential database locks from the two frameworks, but if configured properly, you can get it to work.