or other hostiles.

I always find this to be a bit ridiculous that items pickpocketed from bandits are flagged as stolen, but you can kill them and loot their bodies with impunity.

The same would go for any other hostile humanoids.

Yes. Absolutely. In fact, what I might prefer, and might make it easier, is no steal flag for pickpocketing ever unless you're within a certain (large) distance to a guard. So in cities, it would be same as always, but in the wild, you'd be fine. Similar the the "last witness" idea, how would anyone know? And if they caught you, they've no way of proving it, unless there are guards/witnesses around.