The South Atlantic is fully compatible with ETOPS, they just have to fly a longer route. I read somewhere that SAA's JNB-GRU route is flown with an A332 flying 30 minutes north to comply with ETOPS regulations. So if they are flying to EZE they can't take the direct route, they have to fly to Brazil first then over the South American land-mass to EZE.

Finally there needs to be a reason for this flight. Is there much tourism and business ties?

The only way SQ flies to GRU that they sustain is with the BCN-GRU O&D and allows full payload and capacity between Singapore-Spain and Spain-Brazil.

Finally a-lot of South America business with Asia is done in the US, Miami in particular.