Indeed so, now that you mention it. I also used vdip maps for weird terrains, but never extracted one from a TG terrain. From an obj that would be a different story. In other software you need to have 2 versions of the terrain; one flat, one complete, but - importantly - with the same amount of vertices. Then you bake the difference to an exr.
Something like that, extracting a difference, could also work in TG (from internal terrain, not object). But extracting a vdisp map from TG to use in TG would be quite useless.