You can't use a VM running on Nutanix hypervisor as a RAS template - it's just not displayed in Virtual Guests List window.
This VM was used as a template in the past. It's already marked as a template, therefore it's hidden in the dialog.
- Open properties of the VM in the Nutanix console, clear its description and press "Save":
- Refresh the list of VMs in RAS. The VM will appear there.