Hmm, I didn't think of that. I've only used the technique in a lowpoly workflow. In Transfer Maps you can bake the highpoly diffuse color to a lowpoly, but I'm not sure if it works with vertex color. If it doesn't then a potential workaround is that you just do a quick automatic map on the highpoly and do the whole vertex…
Just thinking out loud here. If the AO transfer map feature indeed is broken, could you not use the Polygon Toolset > Color > Batch Bake (bake override and set to Occlusion) to bake AO on your higpoly. Then map the newly created AO texture on a shaders color channel and use the Diffuse transfer map feature to transfer this…