Can steamOS and steam Link run simultaneously using one PC?

The Steam Link is just hardware that you can stream your games to for cheap. Your PC does the work of running the game while the Steam Link just displays the video and sends input back.

Steam inherently has the ability to stream games to other computers that are logged in with your account, meaning you will be able stream games to the Optiplex with SteamOS.

If you're logged into your account on your main PC, and the Steam Machine you should see the ability to Stream game whenever you look at your library. This will run the game on your main PC, but send you the Video and Audio and send back your inputs