XenServer does not have any obvious stats on the number of VMs in a pool, or on a particular server.  These details can however can be found via the commend line:

Listing number of VMs in a pool (running, halted, or suspended):

xe vm-list  | grep -c running

Listing the number of VMs on a particular host/server (running, halted, or suspended):

xe vm-list resident-on=[host uuid] | grep -c running

You can replace “running” with halted, suspended, or if you want to see VMs regardless of whether they are on or not “power-state”.