This is correct. OracleAQ is expecting it's own DS implementation. While you can call getUnderlyingConnection() from the WrappedConnection Oracle will obviously not call this.
Best solution is probably not to use JBoss JCA at this point. If Oracle expects it's own connection as part of the OracleAQ implementation then you should use their connection pool. It's either that, or lobby OracleAQ to stick to the standard JDBC API.