I don't know, even in OTL SA had a fairly influential Labour Party, especially in the 1920s. It was a coalition between the National Party and Labour which ousted Smuts and the South African Party in 1924. So, in an ATL with a less bitter Boer War it is quite possible that a Labour Party emerges, drawing support from blue collar Afrikaners and English speakers and, in time, from black and coloured people too. EDIT: Read a bit about Walter Madeley, a prominent figure in the Labour Party in the first half of the 20th century. Apparently he represented my hometown of Benoni in Parliament from 1915 to 1945. Not too surprising, Benoni is an old mining town, with lots of English emigrants, so makes sense that an English-speaking left-winger would get support.