Maybe Skittles' survived his encounter with the zombies because of his pheromones. I remember reading that dogs can sense humans who suffer from schizophrenia and some other mental disorders. This is probably accomplished through their sense of smell, which suggests the existence of pheromones that convey human mental states.

We already know how sensitive zombies are to pheromones. Maybe "crazy" pheromones cause zombies to instinctively avoid the broadcasting humans, or even makes the humans invisible to them (like alcohol seems to do).

As for Skittles being a scientist that the troops at Fort Irwin are looking for, I think it's a longshot, but why not. We have no idea who he was before the ended up at the Other Tower. We do know that in the Zombie Apocalypse that lawyers can end up working in the laundry, and salesmen can end up as badass scouts. Why wouldn't genetic science researchers end up pouring concrete?