Theoretically, and I mean it, could someone meet their protein needs from dog food in some sort of unrealistic survival situation?
Protein probably yes, but nutritionally overall not long term. Human nutritional needs and dog nutritional needs are similar but not identical. There are nutrients humans need that would not be considered as necessary in dog food and so, while they might be present in dog food by happenstance, probably at least some are not.
The simplest example of one of these is Vitamin C. Dogs produce that themselves and don’t need to get it from their food, and so including it in dog food would not be a priority. A dog food comprised of meat and grain probably would not contain much if any. But we humans need to get it from our diets or else we get scurvy.
I’m not an expert on human or animal nutrition, but if you’re interested in protein, I think cat food may be the way to go.
Dogs can digest a wide variety of shit. Cats need much higher protein in their diets.