It's just an asset, well an addition to an asset. If this were to be too literal you'd think 3rd party assets wouldn't be allowed at all, as it's someone else's work, whether you have permission to use it or not.
How you use that asset in your art is the question, is it going to add/take from the scenes artistic composition. That's what is being judged ultimately. And if someone were to help you with the composition, atmosphere, or whatever in your compiled scene, than it's more a collaboration on a art piece.
My interpretation at least.