I agree with V de C, except that I would add that if your primary reason for going to South Africa is safari, August is really an exceptional month, especially late August which is really almost the beginning of spring. (We did see Capetown in August, and while I agree it wasn't optimum, it was certainly nice, with one very sunny day and temperatures around 20 degrees C, with terrific views from Table Mountain. And so many of the flowers bloom year round!)
Getting back to Madikwe, while it is cool in the am and pm, the temperature range through the day is probably between 10 degrees and 25 or even 30 degrees C. it can be wonderful in the middle of the day, swimmable. So "winter" isn't what you're probably thinking.
Whatever you decide you're going to love it.