hibernate.jar and cglib*.jar are specified in the lib of the ear. Since, the required jars are within the ear, there shouldn't be any class loader related problems. Also, the required jars are specifies in the ApplicationServer/lib directory, startup script etc
WebSphere has the concept of classloader isolation modes, so I wouldn't be so sure. I'm going to move this to the WebSphere forum, perhaps someone over there can help.