OK, this is new to me, so bear with me.  I would have thought that normal mapping assigned normal vector direction & magnitude, which may be different from the normals as defined in the OBJ.  And while each geometry facet has one normal, a map could assign a myriad of normals across the area of that facet.

     Could a normal map be used along with a displacement map, so as to control the direction of displacement?

     I could see beaucoup uses for such a thing, using a normal map to adjust the direction of displacement.  Using displacement can make stubbly quills on a hedgehog, but they all stick straight out.  With a normal map added, you could make the quills lay in their proper orientation.

     I frequently use displacement to cover large areas of ground with grass.  With an animated normal map added, you could make the grass sway in waves as if in response to wind.

     Same technique could roughly simulate partial derivatives to guide a teardrop streaming down a face.

     Is this feasible? 

     But this would only work -at least work easily- if the normals could be mapped in 2D as with a UV map.  If the Poser normal map is 3D, is it object coordinates or world coordinates?

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5