depends on the pet but sounds like a BAD IDEA. When I was a happy kitteh mama before moving to France, I bought my kitties frozen raw cakes of meat. It was expensive, but I'd read that raw was much more healthy for dogs and cats and it was made by a local farmer, so I knew it was cruelty free. I'm happy to be a veggie and in full support of any one who chooses to be, but you can't expect to sacrifice a carnivore's health over your own omnivorous morals :/
My 2 big dogs eat vegan food mixed with other stufff and my cat eats organic meat food and my chihuahua eats meat food. I chose the veggie food more for their health than my beliefs. What fit in our budget and was the healthiest without unmentionable by-products mixed in.