Just for the hell of it: import your exported hipoly into the scene with your lowpoly, just to check that the sizes are how you need them to be. If your target is to bake a lowpoly vesion then you don't need uvs on the hipoly.
I wouldn't bother modeling these into the lowpoly...my lowest estimate for a lowpoly version that has even the slightest resemblance of the highpoly version would be 4 tris per scale. Hardly worth it...
If you uv map your lowpoly, you can bake the normal from the HP and then texture the lowpoly afterwards. Or you can meshpaint in mudbox or zbrush and bake those down to the maps
Updated omnibeard highpoly a bit Turns out this "lowpoly" mesh I did was 2000 poly, damn ZRemesher:D Still learning modeling, hopefully gonna make proper lowpoly by monday
all you have to do. is do the shake and vac and put the freshness back or load the lowpoly and highpoly objects, put the uvs of the lowpoly in the corect place, and rebuild your normal maps.
I have usually have this occur when I bake from lowpoly to lowpoly in xNormal - try upping your angle bias (is that what it's called?) in your AO settings maybe.