I don't believe I'm following this thread.
Are you saying they log into their machines with their username and remote to the server using the username "domianusers"?
Are you wanting a way for a normal user to remote into the server and not have the option of rebooting or shutting down the server? If that's the case, then this can be achieved by using GPMC and creating a GP under the OU that contains the computer or computers that you want to protect. Edit that OU and drill to the Computer Config-Windows Settings-Local Policies/User Rights Assignment and modify the "Shut down the system" section. Place the users you want to have permission to shutdown the computer.
Close out the windows, click on the new policy to highlight, click on the delegation tab. Add each computer that you would like this GPO to effect. If you don't add the user workstations, this GPO will not effect those settings.
The effect should be users can shut down their machines but cannot remote into a server and shut down the server. I have this set on one of my servers but my settings differ a little depending on how your AD is setup.
Hope this helps.
Justin