What you need to do is mount he snapshot as a different LUN (different signature) to your ESX host. Since it's read only you can copy the VM folder to a different location on another datastore.
From there you can add it to the inventory by browsing the VMX file. Give it a different name in inventory and disconnect the nics or add the nics to a different vlan to ensure that it doesn't boot and cause name/ip conflicts.
