Can a waste drain vent through an exterior wall instead of the roof?

You also have to use the code for your city or your county. Most county and city codes are the same saying that they need to be roof vented.

No, that would defeat the purpose of a vent being that there needs to be air pressure to keep the sewer gas down.

Sure you can, If you want the waste to drip from the vent too the ground, but who cares the Chinese do it so why cant you???

A waste drain vent allows the air to flow so that the drain works properly. It has to meet a calculation that I do not Know, BUT a licensed Plumber will know this calculation. I believe you are asking because this is an unusual situation. Just remember if it does not meet the calculation, you will have nothing but trouble with the drainage. please consult with a GOOD plumber.