Depends on the carb. All carbs have internal bowl vents (in the air horn) and many use an external bowl vent. I have never seen a bowl vent keep the carb bowls from filling as the fuel would still go in the bowls and just vent out the venturi and air bleeds as it would still have atmospheric pressure getting in the bowls and it would have enough room in the bowls to still fill up.
What should happen with an external bowl vent is they are open at idle and should close right off idle. Many newer emission carbs use electric external and sometimes internal bowl vents that use a solenoid to open and close them and some are vacum assisted. Some emission carbs will just have the external vent open with the eng off and closed once the eng starts. Ford had a TSB one time on their 4 barrel carb that if the external carb bowl vent did not close right off idle that the car would run rich when on the gas driving down the road. Thats because it should vent on the internal bowl vents when on the gas since the internal bowl vents are in the air horn the pressure will change from the air running through the carb air horn. Basically the carb should have outside atmospheric pressure from the external bowl vent at idle but driving down the road it will have the pressure on top the fuel change from the internal bowl vent in the airhorn as the airflow through the airhorn will cause less pressure on the fuel because the pressure is rushing into the eng in the airhorn. If you run the correct air cleaner for the car it will work right. The Ford TSB said the car will flood and load up going down the road if the external vent does not close as soon as the car comes off idle as it needs to be closed off idle. Thats basically what they call a balanced carb. But when racers run no air cleaner that does not work so well and the carb has to be jetted accordingly. It can also depend on just where the internal vents are positioned on the carb. Ron