Peter
I live in South Africa and although I do not know much about Orania and some of the "Afrikaner Calvanistic" beliefs, what I can say is this.
Our churches here are quite diverse, unfortunately as in other countries much apathy and charismatic teaching has taken hold, so good theology is looked down upon and much false teaching is rife. The usual TBN etc rule the TV airwaves as well as other popular charismatic teachings. Just like other countries everything seems to be replaced with good old secular humanism. Abortion has been legalised along with p0rnography and now it looks like homosexual marriage will be the next thing.
In terms of the Afrikaner churches while some are good there are some bad. Not all Afrikaners were right wing "Neo Nazis" though, there were those like Beyers Naude that were I believe challenged by God and there christian beliefs and they stood against the shamefull government we had.
http://www.sahistory.org.za/pages/people/naude-cfb.htm
The link will tell you more about him and the work he did against Apartheid. I must admit when I see things like Orania I do hesitate at though, if it is simply a way to maintain a bit of cultural heritage I supppose it is OK, but many times I have to ask is it the true purpose and this goes for black and white. If it is organised by some Afrikaner Freedom movement then I have serious doubts and I can also with reasonable confidence say its part of the old Evil.
As far as the old Afrikaans churches and even some English churches in South Africa and its Apartheid days, you would not have found anything more non christian. Gods word would even be used to support these racist beliefs and you were endoctrinated from the day you were born. Media was controled and the good old propoganda machine worked like a well oiled machine. You sat in school sang Hymns and prayed at the beggining of school etc. You were told you were supporting a Christian country and fighting the commies in Angola etc. But you were not a Christian.
It was a sad time but not all were lost and many new truth and stood for it. Others held and still hold that the white Afrikaners were the chosen ones, I dont know if this is what would be refered to as "Afrikaner Calvinism" if so it is far from Calvinism.
As for me I am a Christian and the only "cultural elite" group I belong to is my Christian family. My fellow brothers and sisters in Christ you are my family black, white , yellow, HIV positive etc. IF Christ is in you you are my family and I hope that the Lord will make that more real to me every day that I live in this world. The only other group are those who dont yet have Christ and they are who i hope to minister to for Christ. Everything else pales in comparison.