I get that its just a skin preset, but it does have something to do with the trait because they dont spawn without gaudy. The game will not give skins like the Ninth Circle to a nephelym unless the spawn with that trait. Spawning with gaudy makes them choose from the patron added preset skins rather than just the normal ones. Try breeding gaudy out of a nephelym while attempting to keep the skin. It wont work because you need gaudy.Though that it doesn't have to do something with the trait, but with the preset like I already said.
Check the Creator Build if unsure, this preset is named "Ninth Circle" and got added for most races. Presets are individual for every race, not related to something like the "humanoid" trait, or the "gaudy" trait, because the game currently picks randomly from all available presets.