In very old fluff (Waaagh The Orks, 'Ere we go, Freebooterz) Orks were not particularly susceptible to Chaos as they had very little for a demon to latch on to, having little actual ego and ambition (if you're big your da boss, if not your the bossed, simple).
Khorne Stormboyz were an option as were possessed warpheads (who were mainly unaffected by their demon aside from getting stronger and letting out sad wailing from time to time from their demon who'd get thoroughly depressed from finding itself stuck in a being completely immune it its manipulations and unable to get back in to the warp)
Your mother cooks socks in Hull!!
If somthing is worth doing, it's worth taking too far, "We set our motley puppets on the clouds and call them gods...","Ah! Now we see the violence inherent in the system!" "Come see the violence inherent in the system!" "HELP HELP! I AM BEING REPRESSED!"
"Quick! Poke it up her "wrongun" before it's to late!" Jezlad