With Sean on this one.
To be perfectly blunt, you're a fool if you're a vegan. Take a look at our teeth - they were meant to chew meat, fruits, vegetables, seeds, etc. We are omnivorous. To deny that for whatever ridiculous scruples people have about eating 'the flesh of a once living animal, man!' (pass the bong) is obviously a step in the opposite direction. Not only that but every vegan I've met has been pasty-looking, ill-looking. We can't survive on that sort of nothing-diet while still being healthy without taking loads of supplements.
To try and force that on your dog is even more disgusting and pathetic. A dog is a meat-based omnivore. Look at their teeth. Canines for snapping through spinal cords, pairs of organic shears at the back for slicing through meat, yet not quite as carnivorous as a cat's, say. To try and go against not only your own but your dog's (which has no say in the matter) natural biology is pretty bad, to put it mildly.
No offence meant to the OP, of course. Your friend probably just needs a bit of a wakeup. A dog is not a toy or doll to follow our every whim, let alone a vegan diet. They're not built that way (and, frankly, neither are we).