Air brakes are designed in a way that the air pressure is required to overcome the spring brakes. In other words, the system must be pressurized in order to be able to roll the vehicle.
That said, I always chock one wheel when at a campground. The Embark jack system is designed in such a way that releasing the parking brake causes the jacks to rise. If a small child in our RV were to push in that nice yellow button, it's conceivable there could be enough air left in the system to allow the truck to roll once the jacks retracted. I realize the risk is remote, however the severity of the situation would be high, therefore not a risk I wish to take.