Do body armors have any effect on the head? Is it better to use hollow point ammunition when targetting a body-armored enemy's unarmored head?
It's been a long time, but if I remember correctly, the armor you have is armor overall, but the Head gets a reduced amount from the armor based on a percentage, and headshots have a multiplier, I believe 2x damage.
So the Armor does help your head, but with a diminished effect. As for Hollowpoint rounds, I think that so long as you can see skin/flesh you're fine.