I'm flying out of Charlotte, NC on June 3rd with my 13 yr old beagle in cargo. Will the temperature in cargo be 85 degrees or higher? If so, I've been told they won't fly her!
Note: your question is not about "normal cargo" but about "live cargo". This requires different cargo position, often accessible by flying personal [but for short flights], and different requirements, not just temperature, but also fire protection: we do not want that CO2 from respiration (and poo) will start the fire suppression system.
For this question, you should contact the airline, and see what they offer you. There is not standard answer, usually you will find a solution [the problem could be the price, for very-non-standard requests].
To directly answer the question asked, “Will the temperature in cargo be 85 degrees or higher?”, more than likely, yes. NOAA has temperature averages for different parts of the Unites States. Charlotte has an average of 86°F. The temperature requirements are probably based on the outside ambient temperature. That is the temperature that can be accurately tracked objectively. The aircraft internal temperature is very subjective.
In the practical sense, the airlines have to worry about several contingencies when transporting live cargo. Where and how in the aircraft they are located is a serious concern. Airplanes, like cars, will get very hot very quickly when parked and unpowered. Ventilation, ease and speed of access will be very important when on the ground. Exposing your dog to high temperatures even briefly is not recommended. Especially, if they are not acclimated.
In flight, the high temperatures are less of a problem. The outside air temperature will decrease by roughly 4.5°F for every 1000 feet of altitude. But, the air density will decrease exponentially. The cargo hold where your dog is placed will need to be pressurized and climate controlled.
Beagles are not large dogs. Have you thought about sacrificing your carry-on allowance in order to have your dog in a travel carrier in the main cabin. Carry a backpack to store overhead instead. Then the dog can be at your feet. Another solution would be to buy a seat/ticket for your dog. I have family members who travel with their husky regularly from New York to Dallas on American Airlines.