You can't put much of anything on top of the track aside from smooth, really thin plastic, such as Mylar, perhaps. It can't even be as thick or as rough as paper.
As for the car in the video, the wheels are rigid, but given it's light weight, the wheels will likely never wear flat spots.
I've also confirmed that the mass of a Z Scale vehicle is too much for it to move, so this will be restricted to sub-Z scales, or objects smaller than Z Scale automobiles in Z, N or larger.