The Oracle probe will use the 'Service Name' you enter in the Connections set up to find your Oracle server.
That server will return values listed in the tnsnames.ora file that would have been set up on install.
Additional entries can be added to the tnsnames.ora file as needed by your oracle DBA.
If that file has been set up correctly, the probe will be able to monitor all instances listed in the file.
If you can use the tnsping utility to ping the install or the sqlplus utility, the probe should be able to see (and monitor) it.
You can only have one setup of variables set up in the robot controller. These variables are to tell the oracle probe which oracle client to use only.
For an Oracle database with multiple instances/SIDs, EACH SID must be configured for each connection profile in the probe/instance, Service Name and Instance must be specified.
***You can specify multiple SIDs (separated by comma, not a semi-colon) in the ORACLE_SID variable defined in the controller probe as the following example shows: ORACLE_SID = oagprod,OAGDEV,OAGTEST,FINEU,OAGEU2,DWPROD,oageu3,oagicrp
but this is not required.
You must also add entries in the single tnsnames.ora file for each instance if that has not been done already and you would need to create a unique connection and then monitoring profile for EACH INSTANCE that you want the probe to monitor.