No, but if the number of units (or unit types) you need to track is relatively small you could put them in a group and periodically check the terrain tile beneath them. A hybrid approach would also work where you put a large region around an area that has some of the terrain tile. When a unit enters that region, add it to the group to check the tile beneath it, and when it leaves the region remove it from the group. Do the same for other general areas that use the tile.