You are likely to get a lot of different opinions on any of this and to me that’s what they are, opinions. To me corn is another potential food source, providing some nutrients and not providing others. Many chicken feeds contain a fair amount of corn. Mine already get corn in a good proportion of nutrient balance with the other stuff in their feed. Mine also forage quite a bit so I don’t worry about trying to micromanage every bite they eat. Since they forage that’s in their control, not mine. But some people like to try to micromanage everything they eat. That’s fine with me, we are all different.
Whether it is whole or cracked is up to you. Their gizzards were developed to grind their food, like corn and other grains. I personally don’t see a lot of difference in ground corn (pure corn meal), cracked corn, or whole corn. No matter what form it is in when they eat it they will get some nutrients from it. If it’s already ground up they will probably get some more so to be really efficient get pure corn meal, no additives. But cracked or whole corn works too.