You don't do either.
Putting the VM ports into Hunt Group 7 will automatically filter how calls are sent to them. Even though it looks like the lines still ring on the VM ports when you look at them through centralized telephone programming, they really don't. Incoming calls are sent through Call Dist Group 7, or Call Coverage. All calls sent to the VM ports are send with "mode codes", strings of touch tone digits, that tell the VM how to handle the call.
The VM ports also get their Intercom Dial Tone changed to "Machine", so that the Itcm DT sounds like an outside DT (so as not to confuse some outboard VM's). Also, the Auto Line Select gets changed to Intercom, Line 1, Line 2, Line 3, etc. If you were to remove the line assignments from the VM ports, you couldn't have outcalling.
An interesting experiment to do sometime is take a system without VM, program one extension port into Hunt Group 7, and observe what it does.