JBoss AS simply passes the connection URL to the JDBC driver - it is the driver that makes the database connection. Does the Oracle JDBC driver you are using support the "jdbc:oracle:oci:@ORCL" connection URL?
Yes, oci has been installed.
The following connect descriptor:
This seems to me to be a matter of the location of the tnsnames.ora file. It is as if JBOSS expects it elsewhere...? Other than the normal $ORACLE_HOME/network/admin
It has nothing to do with JBoss AS. It is the JDBC driver that makes the connection. Can the driver find the necessary files? How do you tell the driver where to look to find those files? All of that should be in the documentation for the Oracle JDBC driver you are using.