While you will find those who have been able to do this, there is no way of telling when someone's bags are not going to get to their resort. Disney's official word is that they are not a luggage transfer service. The luggage delivery is a perk of using DME...so obviously, they intend the owners of the bags to be on the bus.
I, for one, do not want to be the person that tells someone else that they can tag their bags, and then go off in a rental car and be able to expect their bags in their resort room a few hours down the road. Sure, that's what has happened to date, but Disney could conceivebly change that at any time, and I don't want to be the source of bad info.
Either use DME the way it was intended...as a people mover with the perk of luggage delivery....or don't use any part of it and rent a car or use a towncar service.