I believe the air2's have a seperate exhaust port, like any reg. Although I guess it might be possible to suck some of the bcd exhaust back in while inhaling with the dump open. If you lack a pull dump, you're probably going to have to take it out of your mouth for that moment when you press the button anyway.Regarding the BC exhaust, if I remember correctly, if you depress the deflator and breathe in at the same time, you will get air from the BCD, so you might want to keep it clean.
If you use a pull dump, this is a non-issue. Exhaust from the bcd vents at the shoulder rather than traveling down the corrugated hose.