In brief summary, "Yes, but."
To answer my own question, there is some real research on vegetarian diets for canines:
Nutritional and ethical issues regarding
vegetarianism in the domestic dog
(Citation: W.Y. Brown, Recent Advances in Animal Nutrition – Australia 17 (2009))
Summary
Many dog owners wish to feed their dogs a vegetarian
diet for the same ethical reason that they themselves are
vegetarian. To meet this demand, there are an increasing
number of vegetarian diets and recipes available for
dogs. However, proof for their claims of nutritional
adequacy is often lacking. There is little doubt that a
dog’s nutritional requirements can be met from a diet that
does not contain meat; however, the difference between
the amino acid profiles of plant and animal proteins
must be considered. It has been shown that exercising
dogs may develop anaemia when fed unbalanced plantprotein
diets but will remain in good health if the meatfree
diet is correctly balanced. Many plant ingredients
contain high levels of non-starch polysaccharides and
other anti-nutritive factors, which may reduce the
availability of some nutrients. A diet devoid of animal
ingredients is also likely to be of low palatability to
dogs. All diets should be correctly formulated to meet
nutrient requirements based on chemical analysis and
predicted or measured apparent digestibility, should be
sufficiently palatable to ensure adequate dietary intake
and should maintain good health when consumed. If
a vegetarian diet meets all of these criteria, then it is
a suitable diet for the dog, irrespective of the owner’s
motivation for feeding a vegetarian diet.
Conclusions
The nutritional adequacy of a diet, vegetarian or
otherwise, should be based on the ability of the diet
to meet nutritional requirements. Palatability and
digestibility are key considerations. A large number of
dogs are currently fed meat-free diets, and there is a
small but growing niche market for vegetarian pet foods.
The major pet food manufacturers are unlikely to enter
this market until there is greater acceptance of this type
of product. Should this eventuate, it is hoped that their
participation will ensure that the nutritional adequacy
of commercial vegetarian dog foods is validated by
recognised feeding protocols and digestibility trials.
