Question: has vash the stampede killed anyone?
Answer: Nope, he kills no one in the past. About the go Gung-Ho, if your talking about episode "DIABLO", no, he doesn't kill him. No, he does not kill Monev the Gale, he has his arm cannon to his face and then he pulls it away saying, "Rem... Rem..." and he goes off on how no one should ever take a life.