I am encountering the same issue, has anyone ever found a solution to this problem.
It's been awhile, but I did get this to work. The problem is that WebSphere doesn't have the classes for JNP in its classpath. IIRC, adding JBOSS_HOME/client/jbossall-client.jar to WebShere's server classpath resolved it. It then worked great. I had no problem accessing JBoss EJBs from WebSphere deployed apps.
Any luck with the other way around? What if you want to look up a remote EJB deployed in Websphere from within JBoss?