My hens get only layer feed in the coop. (Purina Layena)
However, when it is time to round them up in the evening, I keep a coffee can that is 50% Black Oil Sunflower Seeds and 50% Scratch Grains. I give that a shake and they come running because they know its treat time. The only time I feed scratch grains is as a treat.
The thought behind feeding scratch grains (or any corn products for that matter) during the summer months is due to the high starch (sugar) content and the calories involved require the bird to generate too much heat. Remember: a calorie is nothing more than a measure of heat.
Regardless, I also have several bags of feed corn left over from last year's corn maze. I will generaly throw a few ears into the run every couple of days. Any concern of excess heat has not been an issue for me so far this year. With all the rain we have been having the temperatures haven't been much over 70 and the nights are still dropping into the 40's.
So if you are seeing summer temperatures in Tennessee, its considered best to lay off the scratch grains until cooler weather. They just don't need the calories.