You are right, you do not hear much of the axe in accounts of the AZW.
In Ian Knight's comprehensive, "The Anatomy of the Zulu Army" he explains, " ...the Zulus ....... battle axe, ..... was usually only carried by men of status, and as a ceremonial weapon rather than for fighting." . He goes on to explain that in contrast to the more common half- moon axe blades used by the Shona people of Zimbabwe and the Sotho groups of the interior, and which were sometimes traded into Zululand, " the true Zulu axe - known as isizenze - seems to have been a heavier weapon, with a steeply angled blade, the top edge projecting noticeably above the handle. When employed in battle, it was wielded with a chopping movement, and the lower portion could be used to hook the edge of an enemy's shield and pull it aside.".
If it is of interest, you can see the isizenze in my own collection at http://gallery.me.com/umbiki#100180/IMG_0273 which, incidentally, I keep well out of reach of the woman of the house!
Hope this is helpful.