The trade in promotion is on their site -www.nikonusa.com and has more fine print.
It does not specify only Nikon cameras or lenses. Normally, the legal team would have stroke if they didn’t specify. You could play it safe and call Nikon customer service.
If you don’t have a Z lens at all, you should get one to understand the quality difference. The F-mount lenses work well, but the Z lenses are in a "different zip code” altogether!