You might use DefaultDS for all. I prefere two different datasources.
If you use JBossMessaging the JMS messages might be stored in the database, HornetQ (the default) does not need a database
Also the EJB timers, juddi ... use the DefaultDS, you might remove the services if you do not need it.
http://community.jboss.org/wiki/JBoss5xTuningSlimming and http://community.jboss.org/wiki/JBoss6xTuningSlimming
You might also remove the grant, for the first start you might get the table structure from a test DB (if the DBadmin prefere no CREATE grant ;) )
I think there is no documentation for the tables. But if you do not use the former JBossMessaging and ejb timers the tables are not used.