Hi Adi,
I just searched on Pubmed and this is a recent publication looking at vegetarian diets for dogs and cats.
http://www.ncbi.nlm.nih.gov/pubmed/26225610
If you have a vet that is a member of AVMA you could ask him/her to get the article for you vs paying for it. Maybe it would be of help.
I’d approach vegetarian diets as I would any other diet. Who formulated the diet and what are their credentials. Is there a veterinary nutritionist on staff? Dose the company do feeding trials? What quality control measures are in place. etc.
You can find information on how to pick a diet here: http://www.wsava.org/sites/default/files/Recommendations%20on%20Selecting%20Pet%20Foods.pdf
