Dogs are omnivores and here is what it means...
Omnivore
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An omnivore (from Latin: omne all, everything; vorare to devour) is an animal that eats both plants and meat. Omnivores lack the specialist behaviour of carnivores and herbivores, searching widely for food sources, and are thus better able to withstand changes within their ecological niche. The digestive systems of omnivores reflect their versatility: they are able to digest the components of plants in the manner of herbivores but also readily assimilate protein and other nutrients from meat [1].
Given that brain size correlates to dietary quality (nutritional and caloric density of the diet) and omnivores have a wide-ranging diet, this group of animals is generally an intelligent one. The history of human evolution shows that supplementing our diet with meat allowed the development of substantially larger brains, a process that consumes large amounts of energy and nutrients. [2]. Other omnivorous animals with whom humans interact—raccoons, bears and even crows—often show remarkable intelligence in their food gathering behaviour.
Animals that are true omnivores
Some fish
Mammals
Pigs
Bears
Primates (including human beings)
Domestic dogs
Some rodents, including mice, rats, squirrels, and chipmunks
Opossums
Raccoons
Foxes
Birds
Rails
Rhea
Most gulls
Chickens
Crows
Domestic pigeons http://en.wikipedia.org/wiki/Omnivore
And since some animals on this list do not eat meat throughout their lives i still say that dogs CAN live on a vegetarian diet and be healthy!