GUP Client being out of date doesn't affect its functionally as a GUP and it will continue yo download the serve the definition request that are coming in from the SEP clients provided that the GUP client is have proper established communication with the SEPM.
on a after thought you might want to check as to why the GUP client is out of date. perhaps a symhelp scan on the GUP client will let you know if its holding any corrupt client.