As long as you have IP connectivity, it should work.
'Course it'll be slower than molasses in January (depending on the speed of your VPN), and effectivle, no one else will be able to use the VPN while the backup and/or restore is running, but ...
As mentioned by Ken it is possible if you can access it using the ip address.
You will need to install the remote agent on the machine and enter a remote agent liense for this machine.
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