Youtube in 2018... Well, it doesn't seem like he'll be in trouble with Content ID, ACTA, and SOPA. Unfortunately, youtube's judge that determines that is a computer program that will even accuse indie musician/artists for playing a few notes with a synthesizer, playing an oldies song as a background sample track, or even picking up background noise.
He may get some demonetizing for content showing violence (even if it doesn't) just check any channel that features historical and modern weapons in an educational format.