It is possible with Ploi to use any other server provider then our native integrations. As long as your server provider can install a Ubuntu OS you're all set.
To start, first, create the server with your server provider. After that's done, ensure the created server has a root user and log in as root user.
Next, go to the server creation screen and press "Custom server", it will now show you a command you'll have to run as root user: