The MAC valves we use are rated for both pressure and vacuum. However, if you're using a valve with an air-actuated pilot, you would need to supply external pressure for it--vacuum won't operate the pilot.
To elaborate: Many valves are actually two valves in one. Since the solenoid is relatively small, it actuates a tiny valve called the pilot. Pressure from the pilot is what actually shifts the main valve. (Think of it like a small relay driving a contactor.) So even if the main valve is rated for vacuum, you still need pressure for the pilot to work correctly. With some valves you can specify either an internal or external pilot; internal means it uses whatever is fed to the main valve.