Yes, JBoss supports JCA. It has been getting easier to use since jboss 2.2.2. There is some documentation for jboss 3 in the online free manual, chapter 3. Please ask your questions on jca on the Persistence forum..
In jboss 3, all database access is through jca wrappers for jdbc drivers. There is at least one site that has been using a SAP adapter in production for several months.