Garm effect

It most likely does, but you'd probably already have hone armor or armor march on him if you're using him in an armor team, which is where he is at his best.

It will work with all visible buffs. Waves included.
However, anything that specifically says "during combat" won't work, because that means it's an invisible buff. If it doesn't say that, it will work just fine.

Some Visible buffs include: Waves, Hones/Fortifies, Tactics, Rallies, Defiants.
Some Invisible buffs include: Spurs, Drives, Goads, Wards.