I see no reason not have DMs at the squad level. They are still available to the platoon if needed but they are also available to the squad leader during decentralized ops. DMs aren't snipers. They don't have bolt-action sniper rifles. They are ordinary infantrymen who may or may not have a more accurate version of the weapon that the rest of them carry but who does have more training/skill in engaging targets at longer ranges. He still fights as a regular infantryman but he has an additional skill-set (and possibly weapons system) that the squad/platoon leader can tap into if needed. At least that is how I understand the concept and that is how it makes the most sense to me.

SFC W