The damage still works, but the only way to damage the Khorne units is by moving directly over them. So all you need to do to avoid the drawbacks of the spell is just not move over your own stuff. Which with full control over them, a 8"fly move & the fact that you won't ever be hurt by the aura's really shouldn't be much of an issue. At least if the Khorne units where affected by the aura as well it'd require some halfway intelligent movement. Now there's really no reason for them to ever be hurt. Endless spells are moved by both players alternating, starting with whoever went 2nd this round until you run out of moveable endless spells. It's their main balancing mechanic as that giant vortex of magical murder might end up going back into your own lines if your not carefull. Khorne completly lacks this for some reason.