Yes, you call onepass and they call NW for your upgrades.

As an aside, I find it much easier to get upgrades on NW flights than CO flights.

In fact the only segment I didnt get upgraded on this year was a dsm-msp(232 mile flight) It was on RJ85 that was oversold more than a week before the flight. I can't expect an upgrade if they sell out FC to paying passengers.