Culling strike works with Herald of Ash...

So I just tried it out, everything I cull is showing the herald of ash overkill animation. I thought cull and overkill did not work together?

Culling Strike doesn't Cull if a given hit can kill the target using its Damage instead.

Which is to say:

Are you saying that you've been lowering all of your enemies to 10% of their maximum Life, and then dealing less than 10% of their Life in damage with a Culling Strike - and it causes surrounding enemies to be Ignited? (Do they take damage, or is it a zero-damage Ignite?)

If so, you may wish to take some video and file a bug report.

I suspect it's fine for Herald of Ash to play the animation if you are indeed Culling them instead of killing them with Damage, but not actually Ignite anybody, because that follows the letter of the Gem's law - you'd still be killing them with an Attack, even if it was a Culling Attack, which would mean the skill should at least try to Ignite nearby enemies (and fail to do so, because of 0-damage ignites being disallowed).

I see this might be what is happening. I just assumed any hit on an enemy below 10% health was a cull.