That is a question for your veterinarian who is familiar with the type of Crystals he has or has had. Studies have shown that diabetic cats do much better if they eat canned food and no dry at all. So I would use a canned version of whatever food is selected. The food should be low in carbohydrates to manage the diabetes. Maybe your veterinarian might think that feeding a diabetic food and adding an acidifier might work if that is appropriate for the type of crystal that develops. Some stones require acidification, some require alkalinization.