This i certainly not a JBoss clustering issue...but...the last time I used oracle in that mode, you had to use the Type 2 Driver. Hope this helps.
Think of it this way. One of these has to be true.
1)Type 4- The IP of the database never changes even after Oracle's failover occurs.
2)Type 2 - The Oracle SID never changes (which it doesnt, but the Oracle CLI driver handles pointing the SID to the new IP address after Oracle fails).