I think what daz figures do is stack the uv maps on top of each other that's why you see them together, zbrush doesn't like that at all, so you won't be able to use zbrush to create displacements maps for an entire body… you'll have to use a different program, i think it preserves them though and you can export to something like uv mapper or 3d coat and isolate the maps there
what you can do is create individual maps for isolated body parts, say you wanted to create a displacement map for the head... only export the head, then do your changes export the displacement map it will work correctly in zbrush, because it will only affect one uv map, the head uv map in this case
