Cazadores actually walk and it just looks like they are flying. They are blocked by objects, can’t cross gaps in the terrain or cross rivers (they can’t swim either).

Vertibirds in FO4 are based on the Skyrim dragons and that’s why they tumble towards you when you shoot them. They can definitely adjust their height tho, they do that often to “avoid” the skyscrapers in downtown Boston even tho they can just fly through them. Not sure if it’s the upper part of the building that doesn’t have collision or if the vertibird is just exempt of colliding with buildings tho.