Yes, we use freewheels. The freewheel allows you to rest your feet while the vehicle continues forward, such as down-hill. Then the freewheel grabs when you start pumping again.
The Machine does not know if the terrain is up or down. Nor does it know if the frame is going forward or backward. The Machine only knows that the top of the chain is taut in relation to the drive wheel.
Toy with a normal bicycle for a minute and you will see how it works. You just never had occasion to give it any thought before!
I once rode Henry Ford Goes Surfing with no freewheel -- we had jerry-rigged it after a breakdown. Very scary!
Many tandem bicycles have NO freewheeel between the two riders. A six-stitch injury occurred on such a Kontraption last year in Ventura when one rider started pumping before the other was ready.
There is a clever freewheel that can be a problem solver in some situations: Schwinn once made chainrings with a built in freewheel.