Yes, one can simulate the the flow of car bodies in a wind tunnel.  You have more boundary conditions (I refer to the walls of the wind tunnel) and in some wind tunnels, the walls are porous or slotted which have to be accounted for if your CFD software does not have a porous type boundary condition

CFD analysis should be cheaper also. The engineering challenge in such a simulation is to specify boundary conditions accurately. One thing to consider is the wind tunnel may have some "approximate" boundary conditions to a real life situation that may actually be simulated better with software.

You can very well do simulation of flow over a car or for that matter any automobile. You just need to import a proper geometry corresponding to the real life prototype of the actual vehicle. Also the mesh should be properly made.

Wind tunnel testing will be used as a calibration tool for cad.

Sometimes when there are limitations on the accuracy of the testing conditions like you wouldn't like to invest in a moving belt beneath  the car you can run the cad with the same boundary conditions and than extend to the real boundary conditions