I guess it also depends partly on the type of gritting they are doing, and the nature of use of the gritted surface.
They certainly do sometimes grit footpaths, and it does stop ice from forming (at least on some occasions), so I guess of the right sort of material is used, then it will work.
I remember a few years back seeing a little tiny gritter being pulled along in Wandsworth on the pavements around the Wandsworth Gyratory. I forget what was pulling it (some sort of small motor vehicle), but it was essentially a scaled down version of what you see on the roads, small enough to drive on most pavements.