User Tracking will only get end users connected directly to Cisco switches. If the Cisco switches are trunking to Extreme switches, then the users on those Extreme switches will not appear in User Tracking. If, however, the Cisco switches are connected to the Extreme switches via a simple access port connection, then all the users on the Extreme switches should show up in UT as connected to the same Cisco switch port (i.e. the port that connects to the Extreme switch).
There is no way to add non-Cisco device support to User Tracking.