Currently you really only need one thing to get the job and thats 500 TT to get a work permit. Note thats not a company requirement, but one from immigration. Instructor ratings (any type) sweeten the deal for immigration purposes. Companies like anything that make it easier for the new guys to get a work permit.
As far as practically using your instructor rating, unless you end up in a flight school in Gabs, it will be of little practical use. Company line training pilots don't require an instructor rating. After you've been there for some time and have obtained your Bots license after 500 hrs in the Delta, assuming the company requires it, you may do a flight with the CAAB to get check and training approval for your company.
Having said all this, you could have space shuttle time and be the world aerobatic champion but drinking Black Labels at a braai (bbq) is the best way to get a job. Arriving around this time of year, I would say its easier to get a job than Australia or NZ. Not many new pilots looking these days. If you have 500 hrs seriously just go there, will be the best thing you ever did