It's not so much a "cheat" as it is a strategy. Even in the dark, Soth's men can see the illuminattion of your night-vision goggles in front or the power-pack on your back. To help keep from being seen, take a body (dead or unconcsious) and throw them on your back. When Soth's men are walking up to you in the dark, simply turn and face away from them and the body on your back will cover the light.