Not sure what components you are allowed to use...
JBoss's EJB 2.1 CMP implementation is not based on hibernate.
JBoss's EJB 3.0 persistence implementation IS based fully on hibernate.
Both JBoss 3.x Appl Server and JBoss 4.x app server have integration with Hibernate.
Only JBoss 4.0.2 and higher support EJB 3.0 integration.
People use Session beans for JTA transaction demarcation. Using JTA transactions allows much easier coding as you do not have to manage sessions and connections.
User question -> user forums.