The game does make such a distinction. If an enemy isn’t an screen, then it will never spot Abe or Munch and start attacking them. It’s as though stop properly existing when they’re not being watched. Schrödinger’s Slig, anyone?
Try it out for yourself. Find somewhere with a lot of enemies and try to walk through/past them all while manipulating the camera so they don’t actually show. If you’re patient enough you can get through areas like the part of ‘Dead River’ just before the Storm Circle completely unnoticed.
