Oracle Database Listener is properly configured and must allow connection from the remote host which is Minder Server in this case.
Oracle Connection can be made through Instance Name (SID), database port and privileged username password such as default user is System.
User must have privilege to access system tables and user tables. The minimum user privileges required are: user with CONNECT and SELECT_CATALOG_ROLE roles
While discovering oracle database server, you have to make sure that listener is accepting the connection from remote host. You can troubleshoot the oracle database connection through any database client.