I see what you mean, CS. It looks like he has very prominent withers and his back joins his butt a bit...funky. Almost like a hunter's bump, but not quite. Could just be the stage he's at, too.
As for his hocks...I don't think he's cow hocked at all. He may toe out a tiny bit more than is ideal, but he's definitely not cow hocked. Remember, a horse's back legs aren't supposed to be straight forward. They are supposed to toe out a bit.
Again, it could just be the stage he's at, but I don't like the way his barrel joins his hind end. He looks tucked up in the belly (almost wasp waisted or herring gutted) and his loin (I think that's what I'm looking at...where his flank and thigh meet) looks really funky/weak.