I don't know the internal reason why SA and Gabon would support UN.. however in Nigeria's case... if you factor in the Qaddafi's call for the Nigeria to be divided, due to the situation going on in northern Nigeria.. (rebels are pro -Arab and pro- Qaddafi) then you can see why Nigeria's Government(who are not majority Hausa) would want Qaddafi out of the game.
Yes...I know...which is part of the irony since Kadafi called for the partitioning of Nigeria....which may very well be the result in Libya.
But there is something else which I have yet to mention concerning Nigeria which is a religious factor.