I do think it exsists. However, I think a lot of "examples" of it are just the horse's plain ol' coat though. Like, cream horses (pally, buckskin, perlino, smokey black etc.) tend to have a natural sheen to them. My mare is a palomino, and in the summer she gets pretty darn shiny! I've also seen that in a bunch of chestnuts. I think it's more likely there's something with chestnuts, because not all of them have it and it's just less likely with them. I'll have to take some pictures of my sister's new chestnut QH in the summer because he's going to be like that....
I'm sure a lot of you have seen this picture already, but this is probably the best example of it in the Akhal-Teke breed. As far as I know, this photo hasn't been photoshopped... Google Image Result for http://www.horseartcollection.com/images/akhal-teke1.jpg
If you just google "pictures of akhal-teke horses" a ton like this come up.
Anyways, it's a very interesting idea. I'd love to see if they can prove it.