Ray,  I've had 2 German Shepherds, 1 Australian Shepherd, 1 Border Collie, and 1 Rottweiler since putting in the Ritchie energy free cattle waterers and all of these dogs were able to drink around the floating balls. 

Heck, I've even seen a few barn cats drinking there over the years.  

But I think the Ritchie design is fairly dependant on volume of water turnover through the waterer to help keep the ice from being a PITA.  When it gets really cold, we close livestock away from them at night and put a piece of 1" foam insulation over the balls to keep the ice from getting too bad over night when too few cattle drink to bring in the warmer water. 

I think something like the Cobett water, only with a smaller exposed open surface, would be perfect for dogs.  The comparatively small amount of water consumed by dogs as compared to cattle would dictate a smaller surface opening to cut the heat loss transfer to the cold air.

http://www.cobett.com/

With a large enough heat well, good insulation protecting the well throughout the entire frost zone, and a small surface area to minimize heat loss to the cold air, I'd think your dogs should be able to drink anytime they choose regardless of the temp.

Our cobetts have only 1 - 55 gallon drum for the heat well below the frost line.  Given your location, I'd think 1 would work for this application too.