There is no vitamin deficiency that causes cracked heels. If you were to Google that, you will find it very very commonly claimed that vitamin and nutritional deficiency’s can cause cracked heels. #fakenews
If you do not believe me then just ask anyone with cracked heels how taking vitamin supplements worked out for them (assuming that they did not do something else at the same time to treat the cracked heels). Better yet, if you have cracked heels then start taking vitamin supplements and see how your cracked heels go. Also, there is no scientific study that links vitamin deficiency to cracked heels. Cracked heels are a mechanical problem, not a deficiency problem and are caused by the fat pad expanding out under the heel and causing the cracks if the skin is dry, hard and thick.
You do often see Vitamins C, B3 and E implicated as being issues in cracked heels, but they are not. Yes, those vitamins are important for skin health, but a lack of them will not cause the skin to crack or split around the heels.
By all means try and take vitamin supplements for your cracked heels to see how it works out, or you could do what actually works to fix cracked heels.