Is chop or whole grain corn bad for cows?

Either and both can be just as bad as the other if they're fed in a 100% ration for a long period of time. As supplements to a forage ration to animals that need it, it's not bad at all; rather it's beneficial for the animal especially if the forage fed isn't enough to meet the animal's nutritional requirements, especially when it comes to protein and energy requirements. This is especially true with grazing dairy cattle, be it mature dairy cows or growing dairy calves (regardless of gender), less with beef cattle except for feeder/finisher cattle.