These cars do not have air suspension, they have coil springs front and rear, oil filled struts in front, and oil filled shocks in back. There is a rear load leveling system (ELC), that inflates air bladders that are integrated into the shocks, to maintain proper ride height. If you install non ELC compatible shocks, the rear will sag with any additional weight in the vehicle.
The term "gas shock", or "gas charged" has nothing to do with ride height. Shocks/struts are partially filled with oil, the rest is air. Over rougher surfaces, the air and oil can mix, decreasing the effectiveness of the shock/strut. Removing the air, and replacing it with a pressurized gas, reduces the chance of the oil getting aerated.