This can write only someone who knows nothing about military gear.
At least I can write? Feel free to decide which is a more useful skill.
I admit I don't know a lot about whether a specific helmet can be worn with a headset. What I do know is that there are hats in the game that wouldn't make sense with a headset.
Maybe a solution would be to have a separate 'helmet attachment' slot, and the devs can use their discretion about which gear can be slotted with which helmet/hat.