The galls on Acacia karoo are an indigenous fungus that has always been present in the country. Maybe the increase that you have noticed is due to the drought causing stress to the plants but that is just a guess. It could just be a periodic outbreak of the species. The galls that form on Black Wattle are from an insect (a galling midge) and are very different.
There is one similar biocontrol agent to the fungus on Acacia karoo, that is the fungus used to control/reduce seed of Acacia saligna (often called Port Jackson wattle, but many species are called this). The biocontrol fungus only lives on that species, no other Acacias whether they are from Australia or not. It is host specific.