This was reported here too https://issues.jboss.org/browse/AS7-1151. The NPE is coming from the Oracle driver code, so it's something that needs to be fixed there. Looking at the stacktrace it appears to be doing some MBean registration, maybe it isn't finding the MBeanServer? In any case, that's something that needs to be looked up in the driver source code.
By the way, the JIRA mentions that even with this error, the driver works fine. See if that's the same in your case.