compressed air and nitrogen are pretty much the same thing in paintball. they are filled in the same tank, they have extremely similar characteristics, just compressed air is easier to make. and yes, paintball atlanta has co2 and what is actually probably compressed air.
I play at Gorilla War Paintball just North of Atlanta in Rydal. They got a pretty cool setup there. They're supposed to be adding some more speedball and airball fields but they have a nice arrangement of woodsball fields with some wicked forts. If you've never checked them out you should stop by and do so.