You can get in simply by jumping on a small hill near the railway.
There are plenty of other places for meets and just clearing up driving school will make SF even more crowded (which is undesirable by many players). But I agree that there are large areas around the whole map which could get some use.
And yes, the gate is removable.
wouldnt you normally want a meet in a good looking place for example a car lot or at parking place? also theres an url next to it so if the even happend durring url it would cause massive fps drops and people with lower end pc would need to go to another city
There are tons of better places around the driving school you can use as a meet up hotspot. Think about the one near Zero's RC shop on Garcia or that huge parking space on Foster Valley. Driving school grounds are rather blank and boring. Concrete walls on all 4 sides, what a scenery.
actually that reminds me of "car meet" mode in NFS World
maybe add some spots and when players enter these spots, they can use aerial view to screenshot?
The Photo Is Below 
I Mean Common Is A Big Place And It's Sad To Waste It! 
This Is Just My Idea!