You can displacement map all mental ray for Maya geometry types (polygon meshes, free-form objects (NURBS curves/surfaces), and subdivision surfaces.
mental ray uses an adaptive tesselation approach to better fit the details of the displacement map. The initial tesselation (for NURBS: after surface approximation) is further subdivided to fit secondary criteria, controlled by the displace approximation settings. By default, mental ray for Maya creates appropriate settings that lead to curvature dependent subdivision of the triangles, one form of feature-based displacement mapping. You can change these settings by creating or selecting a custom displace approximation node in the Approximation Editor ( Window > Rendering Editors > mental ray > Approximation Editor).