When I first met Jim Minion, I asked him the same question. His reply was basically, Heavens, Yes! Any time you can have some great basting juices dripping onto a brisket, that is a good thing. The fat drips from the ribs and will help keep the brisket moist. I would imagine it would be similar to when some people put sliced uncooked bacon on top of the brisket for the same purpose?
