It is not possible to use a ServiceContributor when using the OSGi boostrap via OsgiSessionFactoryService. The getService method:
throws an org.hibernate.service.UnknownServiceException. This is due to the fact the contributor is not discovered via the Java Service Loader mechanism. OsgiSessionFactoryService should handle contributors in a similar fashion as integrators and look them up via the OSGi ServiceTracker.
Also, the code should add some error handling. Currently an exception seems to get just swallowed.