I imagine there would be room for both.  I remember one of my favorite parts of the series was how people were surprised (or even outraged) to be presented with (admittedly exotic) people when they went in searching for rare breeds of animal.  It was interesting to ponder just how sentient some of these creatures were, or whether their humanoid appearance was an illusory one or some sort of actual physical change that could only be seen by D, the spiritually aware, or those who have been entered into a contract.  And, of course, the inevitable suffering that comes from a<em>broken</em>contract.