Shore diving on the KZN South Coast is pretty good depending on the season.I am not to familiar with the Illovo area but further down towards the Scotties area I know well and there will always be fish to shoot if the water is clean.
Aliwal Shoal is also a very good option, so long as you catch the Shoal on the right conditions - temp,vis and current.The guys get pretty much all the gamefish species out there - Wahoo,Sails,Tuna,Iggies and the list can go on.There is a guy that offers spearfishing charters to Aliwal and surrounds if you are interested,I can recommend him.
Good luck.