I would say that Deadeye slinger refers to the weapon group Slings (incl Dejeda), however the rogue wouldn't be able to Sneak attack with the Dejeda as the sneak attack entry specifically names sling (the weapon, not group) as eligible. At least that's my take. A proposal might be in order...
SNEAK ATTACK
When you make an attack with a light blade, a hand crossbow, a shortbow, or a sling and hit an enemy granting combat advantage to you...
The thing about themes is, that everybody in Dark Sun gets one, so if we add them here, everybody's got to get one, and not everybody's gonna have all of the access. You can run a character here with nothing but PHB1 (although I don't know that anyone does).