I recommend that you never under any circumstances put anything in the jre ext dir.
Jars in jboss/lib are only those required for jboss boot and are only loaded if explicitly specified, either hardcoded in jboss or specified on the command line.
Jars for your app should go in server/[configuration name]/lib if you never need to change them or server/[configuration name]/deploy if you need to be able to hot-redeploy them and can manage the dependency issues. Unless you do something special starting jboss, [configuration name] == default
Also be very sure you have an oracle-service.xml appropriate for your jboss version. There have been quite a few small changes that don't work on other versions.