Actullay if you look at the watering holes in the grasslands of Africa, lions, gazelles, zebras and all others sorts of prey and predator coexist together serenely. It is only when the lions and cheetahs get hungry and need to hunt for survival do the masses get spooked and run to protect themselves. In the same sense, I could see a mutual understanding coming to both zombies and humans. Although, the humans would always be lower on the food chain and, knowing Maslow's Heirarchy of Needs, a zombie/human coexistence would not survive because lack of security and all.