I am looking at going DAR-JNB-FRA next month on an award ticket from USAir, but the Johannesburg connection is only 60 minutes. All flight are on SA in business class. Is that connection time enough if things go well? I read in another thread that the International-Domestic transfer takes some time due to a long walk, but what about international to international?

Just did international transfers twice in the last two weeks in JNB. Both time on an outside position and arriving by bus.
One time we had to wait about 15 min on the plane for the bus arriving, then it took another 10 min or so to get to the entrance of the building.
Make sure that you dont walk with the crowd to immigration. You need to go to international transfers, which is a walkway outside of the building to the rights. The signs for this are tiny and hidden. Don't enter the building, look for the signs.
When entering the building at the far right side you will see transfer counters to the left and a security checkpoint to the right of the counters. Assuming that you already have your boarding pass go there. One time there was nobody, on time there was a very long and very slow moving line, 30 min wait.
Take an elevator to the departure area, then it is max a 5 min walk to the gate. To get to the SAA lounge turn right, pass the area with the immigration counters and take the escalator downstairs. The lounge is a windowless run down area with some dirty furniture and dirty floors, the worst food i have seen in a long time , some PCs (most not working) and wireless internet (charge, they acceptcredit cards).
60 min should be doable if the line at security is not too long.