Fitzoid,
What you mentioned may be true with the more common LED flood lights, but the newer spot style will cut through like a xenon. I used to carry a Surefire E1e-Ha with the older KL1 LED head (more flood then spot) and when I would use that in very dusty areas (I work in construction) it would have the effect you mentioned. However, I now carry a Surefire E1e with new style KL1 (more spot) and that cuts through the dust even better then the regular Xenon bulb. I'm not sure if smoke is the same way, but if it is the higher quality spot LED lights should fare fine.