Desert dwellers are a nomad tribe, scavenging the vast deserts of their home planet. Constantly searching for water, food, weapons, abandoned tech and scraps of metal, these silent warriors specialize in guerilla warfare, swift and silent ambushes and covert operations behind the enemy lines.
If you wish, you can hire them to join your forces - at a price though. Have in mind though, that a 10 men squad of these fine soldiers is way more lethal than dozens of regular grunts.
After their job is done they simply vanish in the desert, never to be seen again.