For anyone out there struggling with JBoss/Openbase, here is what I found...
(1) JBoss 3.0.2 will not work properly with OpenBase regardless of what OS you run it on. In fact, OpenBase will actually shut itself down on some errors.
(2) JBoss 3.2.0beta2 runs wells with OpenBase but unfortunately does not run on Mac OS X Server. (I think there is a class loading bug in the Mac JVM.)
(3) Watch out for one to one relationships. JBoss generates incorrect queries. To get around this I simply treated my one-to-one relationships as one-to-many.