Not as good, but still beneficial for variety in their diet. They can not extract they same goodness from the vegies because their digestive system is short and primarily designed for a carnivorous diet. To add to that, their teeth can not grind the vegetables like a herbivore so they swallow their food in lumps which makes it even harder for them to extract the goodness. You can assist your dogs by mashing the vegies if they'll take it.
In reality, millions of �s have been invested in R&D on dogfood and you can't do better than feeding one of the better commercial dog foods.
We had a dog who I am sure was a vegetarian. He would rather eat a plate of veg than his dog food, and he loved raw veg too, especially whole brussel sprouts which he would crunch merrily on. He was a large dog and died when he was nearly 14, so they certainly didn't harm him. His teeth in old age were as good as a young dogs, healthy clean and white!!!
I do add some veg and gravy to our two dogs' food bowls when there are any spare. Carrots are a particular favourite with them.
I would be wary of feeding potatoes though in any quantity. I have read somewhere that they are bad for dogs, though not sure why.
My dogs have vegetables every day in with their complete diet. Cabbage, spinach, carrots, beans, with some pasta usually. I dont give normal potato, but have given sweet potato in the past. As long as the vegetables are finely sliced or chopped up small, they can digest them fine. I dont give gravy due to the additional salt content.
My vets have told me that cooked rice, carrots, peas, broccoli are good for my dogs...and they love them!! As a treat I give Lottie raw carrots as she is prone to being a litle large due to her age, being spayed, her breed and thyroid probs!! Lottie munches raw carrots with glee. Pasta is not advisable except in minute quantities (so my vet tells me).
I do use a dried dog food but variety is the spice of life and it has never caused any issues with digestive complaints or wind! I suppose it would depend on the indiividual dog......