You can cook anything you want in cast iron but storing food in non coated cast iron (especially acidic food) is never recommended. If you are slow cooking something acidic like a tomato based sauce your results may vary. Long story short it is not really recommended for tomatoes unless you are only cooking for a few hours or less.Can you make pizza sauce in cast iron? Or is it one of those no-nos like rice?
I'll brown burger and/or sausage in iron and throw in marinara with no ill effects. I will also make lasagna in iron. Once it is cool, I will transfer leftovers to a different container and soak the iron in hot water to get any acidic sauce out of it. I have done cacciatore with no leaching issues either.