Do Saturn sky fluid caps fit other gm cars?

The Saturn Sky was first produced in 2006 (as a 2007 model year).

Chevrolet, Cadillac, Buick, and GMC. They also used to own Pontiac, Saturn, Oldsmobile, and Hummer

Yes, Mustang wheels will fit other cars. For a better answer than that, you could be more specific with your question.

any 68 to 72 A- bodied vehicle.