I recently read a few post here debating about devs pirating game assets, and someone posted saying legit developers pay for everything. Not to further derail that thread, i'm posting a response over here.
I've been a 3D artist for a long long time. There are several art sites where you can put up a gallery of your work.
Almost immediately you'll get requests asking can you do this or that. A few of these sites sell assets, for DAZ, Poser, and other programs. Not only do they sell assets, they allow users to purchase assets and gift them to artists. Quite often I would be gifted sets of items saying "please use my assets in your art" hundreds or even thousands of dollars at retail prices... for simply giving them a mention in the credits. Other requests were people who had a very specific scene that they wanted commissioned. As an example, a request to recreate the scene of a day at the park, when they first met their spouse, intended as an anniversary present. After working out a fee, and list of assets required, they would purchase and gift the assets needed for their render. I obtained a lot of assets, and made a lot of friends in the business by doing this.
As a game developer the same thing happens.... "use my assets in your game" or Patrons pay you to put "their" scene in your game, and I'm not talking about $20 a month patrons. I mean people who foot the entire cost of production... to "re-live their first sexual experience" or "provide an alternate ending, to the one that got away" just to name a few.
Everybody wants to make money, and for those with something to sell... that doesn't happen without advertising. Getting their product seen brings them business. If you want to be "legit" ask if you can use an asset in your game, in return for credit. If you pirate assets, the least you can do is give credit. I would say most will be happy getting free advertising, as long as you're respectful about it. Try not to use their main character, or product in a way that would be embarrassing to their professional reputation or hurt their image, that wouldn't be cool.