Reuse of starship models certainly happened in SF shows and movies. There’s a big fleet battle in Serenity with IIRC some Battlestar Galactica and Star Trek models in the background, and I think the Serenity and one or two Star Trek ships found their way into fleet shots in Battlestar Galactica.
What you're talking about is the same studio reusing assets that they made and have saved to fill in the background.
This is common, but that isn't the same as selling your hero assets to someone else and having them use them as a hero asset, which is what the other person was guessing happened.
