Alright, so I am throwing my hat in and adding another thread to the long list of normal mapping related issues. I am at my wits end on this one. I have checked the polycount wiki, searched the forums, searched the general internet and while I have found many useful things, nothing has solved my particular problem. Here are the screenshots taken from marmoset, and these seams also show up in max on the Xouliul shader.
Here you can see my low poly, the hi poly, the uvs, everything. I have re-baked this thing out of xnoramls 7 different ways, and I even picked up 3ds max and learned how to bake out maps from there, same seam. I originally followed the logical method that I have always been using, uv half, mirror it over, and moved the uvs of the mirrored side off the 0-1. Since then I have tried all kinds of different combinations to get it right. Also tried looking up info on inverted lighting bugs, and that seemed to be caused by either the hi poly or low having its faces reversed before bake, which mine are not. So yeah, I am just out of ideas, if it cant be fixed then I will have to just uv the whole thing without mirroring and that will make my textures cry. Thanks for any help anyone can provide.