CJW I'd say by and large, Americans are HUGE people compared to Africans, even white africans. So by our weight and size, coupled by the fact that the geology of North America is "mild" we do not have much ankle strength and we need the support badly. I've been in places in Africa that looked like the surface of the moon with round rocks slighly smaller than volleyballs everywhere for half a km. No way to step between them and all of them were loose.
I encourage you to be really sure about your level of confidence in your own feet regarding rocks and ankle support.
Second, you need to understand that evolution is quite an SOB in Africa. Nearly every plant and tree has spikes many inches long and every seed pod is so sharp it requires a needle-nose pliers to remove them from your boots. I've spent 30 minutes in an evening pulling thorns and seed pods out of the soles of my boots in Africa many times. The average American shoe or boot like a Merrell is not designed for Africa whatsoever.
As to your feet getting hot, I don't think so. I assumed that the US Gov't knows best about these things so I spent $400 on a pair of the best desert combat boots I could find and I wore them every day for a month breaking them in for safari. I also bought a pair of courteneys and received them at camp in Africa. (I figured I'd wear them at camp and break them in over course of a year before they are safari-worthy) I was wrong. My feet were miserably hot and uncomfortable in the best boot America had to offer. The Courteneys were the most comfortable boot I had ever worn and I switched to them day-2 of the hunt. They have now been worn at least 150-300 days of hunting and I have 6 pairs of them. (I need a 7th) Two pairs are custom made "combat boot height" which I think are even better than their normal boot as they avoid the need for wearing gaiters, and 4 pairs of shoes I wear in the States for casual use.
I would not consider wearing shoes or merrell boots on safari unless you're positive you have the ankles to handle them and you are very, very thin. (marathon runner might be okay)