Two ways you can handle this. 1) Move one set of the overlapping UV's off to the side when you render out the normal maps. Outside of the renderable area. Ben Mathis has a nice little tutorial that covers using chuggnuts UV tools to quickly offset and move back one set of UV's.…
Very helpful tutorial. I used a wacom to make some alphas for a solid colored targa. I used a cylinder with a taper and bend modifier for the tail and a plane detached from the neck and edited to fit around the bridle for the mane. The mane is alright, could be better. The tail is not so convincing.