Would non-human carnivores be able to survive on farmed foods?
The foods people in the developed world typically feed their carnivorous pets (including dogs and cats) are not made primarily from meat.  Instead, they are made from plants, specifically grains, such as corn, rice and wheat.

In order to get our pets to eat foods that are so different from the meat-rich diets of their ancestors, we add flavors to the food.

Check out this episode on the making of pet foods from the television series "How Its Made", http://www.youtube.com/watch?v=220PSFJWHao.

So, to answer your question directly-- yes, in places like the USA, domestic dogs and cats are already living on a diet that is almost entirely plant-based.