The OID for the linux servers will very likely be different than it is on Windows.
What I would recommend is to try the SNMP MIB Browser or MIB Walk tools from our Engineers Toolset (you can download an eval version from the website).
Using those tools you can discover all of the SNMP OID's available to be monitored on the linux box.
Hope that helps.
Can you add a link to this post for the engineer tooset? I wouldn't mind trying the MIB Walk tool myself.
Make sure that the Poller is set for Get Next, or Get Table. If the OID still comes back as unsupported, then the Device is not responding to the OID that you have set. The best way to see what your device responds to is to use our Toolset and perform a MIB Walk.
MIB Walk will discover and produce reports detailing which MIBs and OIDs are supported on a particular device. For more information about MIB Walk see the Toolset's Administrator's Guide on PDF page 324.
You can download the 30 Day Evaluation here: Evaluation of Engineer's Toolset
For more information about the Universal Device Poller, please see the Online Administrators Guide here: Universal Device Poller Online Guide