Hi,
If i understand well. My guess, you should export the mac address , because when a VM is copied, and then start, vmware will generate a new mac address (You could not have 2 VMs with the same mac address connect to a vswitch or a vDS. So you will be able to compare the mac address. But this work only on the same infrastructure. If your client export the VM and re-import on another infrastructure, the vm will be exactly the same.
Regards,
Julien.