Dog digestive enzymes are made for owners who want their dog to get the most out of their food. Working dogs especially can benefit from better digestion and nutrient absorption.
But as for dogs with diarrhea, something's wrong. After a trip to the vet, it's time to deal with the symptoms. Hydrate your dog by giving him lots of water, and give him a diarrhea support designed to reduce and treat his diarrhea symptoms.