I cast EntityManager to HibernateEntityManager.
I should add that I do this to get the current Hibernate session.
Never mind, after some more searching, I figured it out.
I was doing
Session session = ((HibernateEntityManager) entityManager).getCurrentSession();
When I should've used
HibernateSession session = (HibernateSession) entityManager ;
(or something like that...)
I did notice that the HibernateSession is still packaged under the jboss package hierarchy, as opposed to org.hibernate.
You can also inject a Hibernate session directly, by doing something like:
private @PersistenceContext Session session;
Check the JBoss EJB3 docs.