The vehicles seen on the parking customization will reflect the airplane profile used so, in your case, if that airplane doesn't call for a vehicle, because its profile says so ( or you are not using any profile ), you will see the pointer but not the vehicle.
This is of course entirely normal and intentional: by seeing the pointer, you can still customize the parking without having to load or even own an airplane that would use that vehicle. If your airplane can only use 1 stairs, you can still customize all 3 stair positions, for airplanes that can use them, even if you won't see the other stairs with the currently loaded airplane.