If you want mutated elephants, then that's exactly what you can have, until the devs go their own way, which I doubt they will with a region like Africa. So go nuts
I doubt Africa would have been so badly hit, it wasn't really a main player, it might have got caught up with some shockwaves though, thing is radiation doesn't travel very far, so unless it was directly hit there wouldn't be any radiation and thus no radiation based mutations. But again, it's completely unknown. All we know is pretty much the whole world got hit, but there can be exceptions to the less populated regions.