The only issue I could see is that you are asking an air pump to become a miniature air compressor...... It would require at least a few psi to drive water from a sealed vessel to the tank. Since most air pumps are just simple rubber diaphragms, I'd have my doubts unless you're using a small piston pump.
Interesting idea, but at this point, it's sounds like it'd be getting too complicated for the effort..........
Wanna calculate the cost of that new reef tank?? Take your worst nightmare, double it, and you're halfway there.