Alignment is always in the eye of the beholder. ...And it kills you with its eye beams, every time.
If he has no choice, eat human or die, then how can you blame him for wanting to live for eating someone who is already dead? Intelligent creatures in this world eat other intelligent creatures in order to survive and they're not evil. Look at the Dragonne, paragon of good and it looks like it eats people... evil people sure but people still.
As for the witch example I would assume part of the hex casting is naturally evil, but eating rations made out of human for a half-orc is probably okay... so long as he's not going out of his way and just scavenging like you mention.