The default com.arjuna.ats.arjuna.tools.osb.mbean.ObjStoreBean does not initialise itself properly when running in the AS causing a null pointer reference when displaying the bean in a JMX client.
Also the need for the jmxEnabled property of ObjectStoreEnvironmentBean is superfluous.
See workaround for how to initialise the bean via transaction-jboss-beans.xml.