I've never fed the yorks raw, but I used to feed raw to my kitties and my medium-sized mutt. I did the BARF diet thing and mixed everything at home; much cheaper (but then, if you're feeding one yorkie, maybe you can afford to skip the mess/trouble of home prep). This was several years ago, but if I recall correctly, they emphasized that you don't mix raw with cooked foods, due to the rate of digestion and the likelihood of upset tummies.
My girl did extremely well on the diet, and huge plus -- her stools were much smaller, firmer, and disintegrated within a few days...no need to poop scoop LOL. Her teeth absolutely SPARKLED and her coat was amazing. I would still be feeding it if I had a place to store 30 lbs of chicken necks at one time.
Ash