The major similarity would be that both the colonization of Vietnam and the apartheid system in South Africa were imposed on the natives of the area by outsiders. In that sense, then, the struggles were similar because they were struggles against outside oppression.
But the differences are great. The most important is that, by the end of their struggle, the Vietnamese had support from other countries (China and the USSR) and were able to wage an actual military struggle against the French. By contrast, the anti-apartheid struggle was largely a non-violent one (on the part of the anti-apartheid side, at least). It was supported by outside countries, but only in moral ways like sanctions against South African sports teams, not with weapons.