On the Gateways page, there's no data in the users column in netscaler monitor.
There are user when looking in the netscaler itself.
You looking for the number of active HDX sessions?
In the dashboard I can see SSL Users, if I click on the Gateways in the left menu I can see the list of gateway but the Users column is empty. I can see some of the users under HDX sessions but not all users and not associated with the gateway.