Having checked around, I'd say that while feeding a veggie diet to a dog bespeaks a certain excess of zeal, Hawthorne won't necessarily suffer any harm from it. Though meat eaters by nature, dogs seem to adapt to a plant diet reasonably well, the main challenge being to make the stuff palatable enough that they'll actually eat it. Some believe dogs have a greater need for meat-based nutrients during stressful times of their lives, such as puppyhood and pregnancy. During these times, and maybe all the time, you might want to use diet supplements or a specially formulated veggie pet food such as Nature's Recipe. Only a fanatic would keep a dog on a veggie diet if it obviously were failing to thrive.
Cats are another story.
It's dangerous and probably futile to try to feed a cat a vegetarian diet. If denied meat at home cats likely will go hunting for mice and birds and whatnot. If unsuccessful, they may suffer serious health problems. Cats require specialized micronutrients abundant in meat but not readily available from other sources. Other nutrients they obtain primarily or solely from meat include arachidonic acid, vitamin A, vitamin B12, niacin, and thiamine.