The purpose of an expert is to assist the court. Not to testify for the defense or for the prosecution.
So, in theory, this means that an expert must give all information he gathers to the court. No matter who is paying. Wolmarans is giving his expert testimony. Without prejudice. Honestly. His peers, and everyone who's worked with him, confirm Wollie has a lot of integrity. And he is very experienced. Those two things, honesty and experience, give him a certain cachet, not only nationally in South Africa, but also internationally. (Yes, his English is horrible. His grammar. The way he speaks is boring. But that does not mean he's stupid.)
I'm starting to wonder if the delay was because the defense was looking for someone else to present Wolmarans' testimony in court. Someone like Dixon who was perhaps prepared to put the evidence in a more positive light for the defense.