As his job skills are much in demand he may be able to get a job offer whilst still in SA but, as Beth says, it is a lot easier to find work when you're actually in NZ and potential employers can see you've already made a commitment by visiting the country.
If he has enough points i.e. 100+ to apply for the EOI he can do it without a job offer, but some people don't have enough points to apply and need that all-important job offer to give them a boost. If he gets a job offer after submitting the EOI, he can inform INZ of this and they will amend his file accordingly.
If he wants to go to NZ before his application for PR has been approved and/or before he's got a job offer, then he would probably have to go on a Visitor's Visa, look for work, then apply for a WP to allow him to work in NZ until his PR comes through. It's advisable not to alert Immigration that he's there to look for work. A VV is supposed to be used purely for visiting
.
If he finds a job without having to go to NZ and before his PR comes through, he could apply for a Work Visa on the strength of the job offer and enter NZ on that. The WV will be converted to a WP on entering the country.
I would clarify that the latter 2 comments would also apply even if he didn't submit an EOI.