With the South African Springboks beating the New Zealand All Blacks on 15 September 2018, Rassie Erasmus has joined an elite group of rugby coaches who can say they have won test rugby in New Zealand. That made me wonder how many coaches in the world have won test rugby in New Zealand in the professional era?
According to this query on ESPN Scrum, New Zealand has lost 10 times at home since August 26th, 1995 (the beginning of the professional era). The coaches aren't mentioned but can be retrieved from Wikipedia.
Team Score Opposition Ground Date Coach =========================================================================== New Zealand 3 13 v South Africa Wellington 25 Jul 1998 Nick Mallett New Zealand 23 27 v Australia Christchurch 1 Aug 1998 Rod Macqueen New Zealand 23 24 v Australia Wellington 5 Aug 2000 Rod Macqueen New Zealand 15 23 v Australia Dunedin 11 Aug 2001 Eddie Jones New Zealand 13 15 v England Wellington 14 Jun 2003 Sir Clive Woodward New Zealand 28 30 v South Africa Dunedin 12 Jul 2008 Peter de Villiers New Zealand 22 27 v France Dunedin 13 Jun 2009 Marc Lièvremont New Zealand 29 32 v South Africa Hamilton 12 Sep 2009 Peter de Villiers New Zealand 21 24 v Lions Wellington 1 Jul 2017 Warren Gatland New Zealand 34 36 v South Africa Wellington 15 Sep 2018 Rassie Erasmus
Two coaches pulled it off twice, so the answer to your question is 8.