"I am wondering how the name Nivison could be Gaelic or Scottish if it is impossible to find its association with any of the clans?"
Nivison is just a semi-translation of MacNiven, like Nicolson of MacNicol (sometimes), Farquharson of MacFarquhar (always), Donaldson of MacDonald (always), and so on.
Clan booths at highland games will obviously not cover all the hundreds of Scottish surnames. In the case of Nivison the name takes its place with the numerous Gaelic names of the Southwest of Scotland, dating obviously from the time when Gaelic was also spoken in Galloway (up to the 17th century). In the cases of Nivison, Farquharson, Donaldson the bit before the "son" is simply a Gaelic language name.