No, the heat is horrible from May through Sept and it's only getting worse. This year has been an exception but for the most part, you want nothing to do with being outdoors for any extended periods of time during those months.
Six Flags and Seaworld have parks in Dallas and San Antonio (Houston used to have Astroworld), so its already been done. That being said, you wouldn't catch me dead in any outdoor park during the summers here.