Hi Renan,
usually MWS should be able to use the branded DataDirect Driver bundled with the wM Suite.
Same applies to the MWS and CentralUsers functions under the JDBC Pools section of IS Admin.
Make sure, that you use the URL format starting with "jdbc:wm:oracle://" for your Oracle database connection.
Please note, that the DB connection used by the MWS itself is not configured via IS Admin, but in a file called "MWS/server/default/config/mws.db.xml".
Additionally check, if you have applied latest Fix for DataDirect driver along with your update. There might be a compatibility issue, when not all components are on the latest fix level available.
As 10.3 sounds fairly old, you should consider upgrading to 10.15 (last version provided by SAG, before IBM took over the wM Suite).
Regards,
Holger