Attorney Ulrich Roux on the local SA Channel 199 says that SA law forces the state to give the defense team access to the whole docket, but the defense is technically not legally bound to give the state access to anything. However it is usual to supply the state with expert witnesses' reports in advance. The fact that OP's defense team has not done so is very unusual and could even be called "highly unethical."
Ulrich Roux also says the fact that Prof Derman did not supply a report at all forced the state to rely on Dr Carla Kotze and so the defense is not entitled to consult with her. I think that the whole thing with Dr Kotze was a fishing expedition by the defense to see if Nel plans to reopen his case. Roux said that all Nel had to do is say that he plans to call her as a witness.
Ulrich Roux also says the fact that Prof Derman did not supply a report at all forced the state to rely on Dr Carla Kotze and so the defense is not entitled to consult with her. I think that the whole thing with Dr Kotze was a fishing expedition by the defense to see if Nel plans to reopen his case. Roux said that all Nel had to do is say that he plans to call her as a witness.