I don't think that sewer gas rises out of the vent pipe like you think. The vent pipe is there to provide an equalizer to the rapid pressure changes that occur in your plumbing when you drain a sink, tub or run your dishwasher or washing machine.
Without a vent pipe, draining your sink could cause a nearby tub (or other fixture) to start filling with water through the drain. It can also cause your p-traps to get sucked dry leaving sewer gas free to enter your home through your drain.
I'm no plumber so I could be wrong, but that is my understanding of the purpose of a vent pipe.