A displacment map is just that .."A Map"...it is not an actual part of the mesh.

The issues at daz are if you use their mesh for making things, wether this is cutting parts out for things like geografting or shrink-wrapping a new mesh to their sculpted shape.

But all a displacment map does is give the renderer instructions as to how to render the object. Just like Diffuse maps, Spec maps, or normal maps (and any of the dozens of other maps you could include with an object.

There is nothing illegal about making displacment maps.