I thought necklacing was a Winnie Mandela legacy, not a Nelson Madela legacy. Winnie was evil incarnate.
What isn't debatable is that Winnie visited him regularly during the prison years and used him as an icon of ANC resistance at the time. I find it hard to believe that they did not communicate about such tactics, but I suppose it is possible.
Their marriage lasted until some years after he was released from prison. Many like to believe the end of the marriage marked the end of such brutal tactics by the ANC. Time will tell.