An OSDT's helmet does more than just conceal one's identity or hinder head shots. IIRC, in Cole Protocol OSDTs have HUDs of their own (which I'm sure Recon will backup), so why would they need a red dot sight on a weapon when they have a system that works just like a spartan's HUD? Kinda doesn't help the whole "oh well its a fallen OSDT's SMG" defense...