I love seeing non conventional breeds succeed. Though you will see a common conformational theme with any horse that makes it to the upper levels. The upper movements require a horse that can sit on it's hocks and collect, but still have the suspension and extension. TBs still reign supreme in my book for eventing. They are lithe in the dressage arena and galloping machines. But if I was looking to just do dressage, I'd have to go with a WB. Though I think there's a Mustang out there that is giving the blue bloods a run for their money.
Now I have to go find tissues as my eyes and nose are running from laughing so hard at the Men doing dressage video.