I got a reply privately from the owner of "Eddie's Wheels" who was opposed to motorizing their rear wheels for a paralyzed dog.
Their logic was that Eddie's wheels were designed to be a walking aid, and that power assist would allow the dog to weaken the legs that could function.
Actually my desire to motorize the dog's rear wheels is motivated by my wife's desire to go hiking with the dog. And as things are now, they cannot walk together for more than 200 feet before the poor dog is exhausted.
The idea of using a geared down electric power drill (12-20 volt DC) with it's chuck is a good one- thanks for making that suggestion.