Don't worry! We also got married in July @ Olander. It was hot as all get out. Our wedding cake pretty much melted, my MIL missed our dances because she was in the car with the air...but DH and I had so much fun.
All the people who we loved and adored stuck out the heat with us. Don't let anyone get you down!! It's gonna be a complete blast and if not you'll have funny stories to tell. They let me get dressed in the office and the office has AC.
If they are predicting warm weather tell everyone you already know and not to mention it again. Seriously, I got more then a few phone calls asking if we were still having the wedding because "It's gonna be so hot on Sunday."
hehe best advice...order a pizza on your way out of the reception. We were both starving at the end of the night!