This idea is not really required for GUP functionality.
GUPs don't provide updates to other SEP clients from their own definitions, but rather have a separate repository for definitions provided via the GUP feature (as per http://www.symantec.com/docs/TECH102541). As such, GUPs are not required to already be on the latest definitions for the other SEP clients to obtain the latest defs from them.
Case in point, you can lock a GUP to yesterday's definitions (using a separate LU Content policy), but it will still be able to provide today's defs to other clients.
#EDIT#
As an aside, despite it not being required, you can generate the behaviour you've described by putting all your GUPs in a separate group and changing that group's "Communications Settings" to use either PUSH mode or a smaller Heartbeat interval. This means the GUP are more likely to be aware of the latest definitions earlier than other SEP Clients.