Considering the number of messages I have read over the years about people who grew in corn fields losing their crop or being busted I think it is a less than intelligent choice to make to grow in a corn field but the part about corn being long gone before a herb crop would be ready to harvest it only speculation. It would depend on a good number of things.
As of the 12th of this month only 51% of the 18 top corn producing states corn crop have been harvested, and that is up 38% from 2009. Lots of harvesting comes later than people think. If the person knows the field he would plant in is always harvested late in the season he could pick a strain that could finish in time. It could in the end go either way and they could lose but there is a good chance that the corn would not be "long gone" by the time his plants were ready to harvest and it could be pulled off ... IF the grower gets very lucky in regards to all the other possible risks.
I would never risk growing in a corn field but I can see why some people think it would be a good idea. Tall plants around other tall plants making them all blend together so they do not stand out, in a farmer's field where people seldom, if ever, take a stroll and if they do there is so much acreage that the odds are slim it would be where their plants are. It can sound like a darn good idea to someone who has never learned about how many people lose crops and or get busted by trying to grow in some farmer's field.
People should stop breaking his balls over it and let him do whatever he wants. He just has to realize that when he plants in a farmer's field he's made his bed and he'll have to bang whatever crawls into it ........ even if it is really fugly.