I was coming in here to say this: every MGS since they added the stamina bar I have beat non violently, including all the bosses. Even in the MGS 1 remake Twin Snakes for GameCube, no kills.
In MGS 5 they have a whole set of non lethal shotguns, sniper rifles, and assault rifles. I think it's super fun, and makes you come up with creative ways to knock out armored enemies.
Ah my bad, I'll correct it.