I used to think that the who system was sealed. After my car was rear ended though the line that goes to the trunk got cut. When I would lock or unlock doors air would escape or get sucked in. All the locks still worked though. Later a patched the line with some tubing but it lead me to think the each unit on the lock must make its own vacuum.
1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500