With vSphere
Backup:
1. Convert the VM Template to a VM
2. Take snapshot of the VM
3. Backup the VM as normal VM using vSphere APIs and VDDK APIs
4. Convert the VM back to a VM Template
Restore:
1. Restore the VM using vSphere APIs and VDDK APIs
2. Convert the restore VM back to a VM Template
With NetVault Backup
*To backup via NetVault, you must do the same, which is to convert the VM Template to a VM, back it up, then convert back to template.