I haven’t been able to find info on this, but if I were to put dirt and grow grass in my sulcata’s enclosure would that be safe for them? Or would just normal substrate be better?
If you plant seed directly in the substrate it will be trampled or eaten before it can get going. And grass also doesn't do well indoors unless you have some serious lighting going on.
I'd get a few shallow trays, use some additive free soil with no perlite or water retention stuff in it, and start the grass in a sunny area outside. Then make a spot in the substrate and set a tray down in it so the rim is about flush with the substrate. Then you can trade out trays as one gets eaten. You can keep rotating trays and letting each one recover and regrow as the others get eaten.