Attached Link: http://hexablog.eovia.com/video/hex2_napoleothon.mov

It is not a render time displacement map as you can see in the video clips it happens in realtime and it is displacing the geometry. But the question was can you displace soo much that you endup with horns? Well it would be faster to just extrude the horn and use the displacement mapping/realtime displacement to add the details like in this video. http://hexablog.eovia.com/video/hex2_napoleothon.mov So yes it does add geometry that is why you model can be of large polygon count.