I understand how good the Darkstalker feat is in combat, and for melee characters it's basically required. But can the same be said for ranged characters and stealth out of combat? How useful is it then?
Darkstalker is necessary if you need to sneak around things that have special senses that would otherwise auto-detect you. It’s pointless if you don’t need to do that. This is true both in combat and out: whether you’re sneaking up on something to stab it or sneaking past it to get whatever it’s guarding, you need Darkstalker if it has special senses.