I dunno about other universities & tech but if you went to uct and cape tech(but then as i say cpt has always been way ahead from bottom up) you'd know that there is little need for AA in engineering! The majority of students are non-white and in some instances the % african foreign students in masters up is pretty high % too. Then combo this with scarce skills visa + DoL being a bit more lenient on the sector giving lots of concession and you have to question the continuous rants on this forum. (bottom up that is, top down is an entirely different story and eng people take longer to change as exp is key).
When organisations go for a heavy AA recruit drive, check out their current employee's (top down remember % weight for top is more) and you're likely find that they are heavily unbalanced(hence rec drive, and usually they go all out so the numbers look better) but even so if a suitable person can't be found the position -has- to filled. I think this past year may have been 1st time in 15yrs that positions are becoming very scarce for grads, competition is rife and positions didn't need to be filled and were reduced.
There is a problem with pr eng though but its not that there aren't candidates, its just that the system loses eng graduates to other industries with attractive packages + they need to improve their integration.
I'm not sure if I'm misunderstanding your point but non-SA citizens don't qualify for AA even if they are from Africa.