These guys are from 8th and I Marine Barracks, Home of the Silent Drill Team. These Marines aren't on that team, but the drill competency of that whole unit is unreal. They probably haven't heard a cadence except for fun for years.
Marines don’t salute indoors unless under arms. Those Marines are not under arms. Marines don’t wear covers indoors unless they are on duty or under arms. Those Marines are on duty so they are wearing covers.
If a Marine is wearing a cover indoors, he salutes. He usually doesn't unless under arms, that's true. If he is covered he salutes. Marines are ALWAYS on duty if they are alive even in civvies. If you are covered for whatever reason you are saluting should the need arise. Part of the 11 General orders. Under arms also consists of the duty belt, hence the cover. This does present problems with other services' General. From experience.