The screensaver settings are set in the 'User Configuration' section of a GPO, and therefore apply to the User objects in the domain, not the computer objects. Moving the computer object around and blocking inheritence to that object will have no effect, since it is the user account which is logging in which the policy is applying to.
The only way you can work around this is to move the users who will need the ability to change Screen Saver settings into their own OU out of scope of the GPO (either Block Inheritance or adjust your OU structure so they don't inherit the OU). This will, however, give them access to change their screen saver wherever they go.
The other approach in some cases would be to disable the restriction just on this one server by creating a new GPO on the server's OU, overriding the screen saver settings to 'Disabled' and then enabling Loopback. The problem here is this will simply do the opposite and turn off the screen saver; it won't enable you to unlock the settings so changes can be made.
-Matt