Sure you can add one or more nodes to the database as "bare metal" use the MAC address as the name. Schedule a provisioning template and then drag the new machine to the task and start it. When this machine boots to your provisioning media it will start to deploy your provisioning template.
You could take this a step farther and create a query that looks for the new bare metal devices that haven't been provisioned and adds them to the provisioning task every hour. This could get tricky if the machines don't get taken out of the query you could wipe out a good system next boot sequence if not configured properly to boot from HD first. Make it so you have to press an F key to select alternate boot option.