Not dumb at all!
I just gave my dog some soy crumbles yesterday. When I make dinner I add anything to her dinner that seems interesting (she has very little appetite, so we coax her a bit)--plain pasta, brown rice, plain chicken, plain veggies--pretty much anything except dairy (dogs are basically lactose intolerant, or so I've read) and sauces. Boy, that was a great sentence. Anyway, she liked the soy and I haven't seen any adverse effects. I know there's vegetarian dog food, and I imagine it must have soy protein in it, and tofu and soy are plant-based products, so I think you're in good shape.
This is all based on reading and random impressions, so someone please correct me if I'm wrong.