No need for that. The configuration management of NixOS is baked right into the installation procedure. This makes it super simple to install a fresh machine completely from the configuration.nix file that you've developed over time.

Well, with an OpenVZ VPS, the most common variety these days, you'd have to have it offered by the provider.

Ahh, I would never use a VPS that didn't let me use my own OS install image.

I don't have any information about it, sorry.