I've done brats in beer many times over the years, but never in a slow cooker, always on the stove.
However, If you're worried about the beer smell, I bet this would be a great application for sous vide... Dogs/brats in the bag, shake most of the fizz out of the beer and add it, and throw it into the sous vide bath for however long.
Finish on the grill?
Hell yeah!