Nelson Mandela went to prison on charges that he urged black workers to strike (stop working under apartheid rule) and that he left South Africa illegally. At the time he was publicly declaring his intention to dismantle apartheid with nonviolent action.
The prosecution, and the sentencing judge, described these as terrorist acts. They, like the white supremacists you cite, sought to undermine his moral authority, and thus his political effectiveness.
I take it you are asking whether Mandela gave his blessing to bombings that occurred while he was in prison.
What evidence do you expect to find? I see you've already determined that the claim that he admitted to complicity in his own book is a lie. Have you otherwise looked for anything other than accusations?
I find the accusations absurd and contrary both to his professed beliefs and his actions. He resisted the push for armed resistance from other factions of the ANC, and after the collapse of apartheid he championed a policy of forgiveness and reconciliation, even for those who committed the worst abuses against black citizens of South Africa.
Debating whether armed resistance by the ANC could be considered terrorism might be interesting--
are there any unarmed civilians in a society that profits by using thugs to exploit, oppress and murder an underclass?
But treating white supremacist web-bile to serious debate on the occasion of his death seems to me only to serve their racist propaganda purposes.
So aside from these observations, I won't.
"If you can keep your head while those around you are losing theirs, you can collect a lot of heads."