Well not sure why but this question interested me as I had just happened across a short article on the 9.3 and some wildcats built off it.
So I just did a quick search on the africanhunting forum. Many of the active members there have been going on African hunts for decades.
https://www.africahunting.com/threads/9-3x62-for-cape-buffalo.10705/
https://www.africahunting.com/threads/9-3x74r-legal-for-buffalo-in-south-africa.29913/
There are about 50+ threads on a number of forums and probably 100s more if I went to a second page of a google search. But this last thread link above I think gave official links as well as description about how the regulations actually work.
In some cases and places its 375 in others as was mentioned its a joules limit which apparently some may have met with hot handloads. But if you read down thru the thread you will see where they discuss diff in how regs are applied for public vs private reserves. It seems in sone providences its up to the reserve to set limits and any rules that cover these area are more about things like poaching with .22 cal etc. Its pretty evident by any lack of rebuttal/disagreement on a forum with tons of very experience African hunters that yes you can use the 9.3 on cape. Not to mention quite a few first hand accounts with numerous photos of cape trophy kills using 9.3.
If this was a big no no then there would have been a large negative response there as I have seen it in the past on things that are a no-go.
I have no dog in the hunt about your debate but was curious.
I, personally have no intention of using anything smaller than a 375 on my dream hunt when I turn 50. I tend to error on the side of a healthy cushion when it comes to things with the price tag hunts like this cost in total . For my bull cape the 458 Lott will cone out of the scabber. 470-500gr @ 2250-2350 seems to be the recipe. Either north fork or maybe have Hammer spin me up a pill or CEB. I have shot loads like this before
while stout are doable for 1moa accuracy off tri-sticks when the heart is pounding.
But it does seem and as proved by photos that the 9.3 can and is used to hunt cape on various reserves in Africa.
I'm out.......