I have used arrow units from all different positions. I have not attacked a settlement recently but during my attack there was 0 damage done. I used fire arrows in a follow-up attack on Nok Rassol and there again was no damage vs the orc archers. I have attacked both Elven and Human Settlements and Castles and both types of sieges I was able to kill the enemy units on the walls including archers and siege weapons. However none of the orc units have ever taken a single arrow from my rangers, i have not tried with Female wardens but I do not build them.
I will try to get more information but as of now the seiges vs Orcs is much harders as I can only use melee units. I first have to destroy gates and walls (since orc only have wooden walls) and simply smash my way through.