I got what you got. All those black splodges. I think what it is, 3dcoat shaders are sort of only for 3dcoat, did you use "metal" shaders. they dont really export as anything. So that maybe a limitation to vertex paint to Blender. They look nice in 3dcoat but you cant export them because the use the "effect" of a bump and specularity. When I do metal I usually do it in Blender rather than 3dcoat first, but I just do simple stuff like gold earings and buttons.
I think you should experiment a bit more. Just make a sphere and experiment with that. Vertex paint it, export it. Then retopo it , and export the maps that way you can see how it all works. FBX to Blender works just fine and stores the colour infomation. All these effects are probably easier in Blender if you retopo and bake various maps that you can adjust with alphas and all the stuff, but they are a pain to make. Vertex paint is easier but then you have the limitations....there is always a catch isnt there.
Im sorry I cant explain whats taken me years to learn in a couple of paragraphs. Ha Ha .
It took me ages to figure out the Vertex paint to Blender thing, there didnt seem to me any info anywhere. But since I figured it out I mix and match depending on my needs.