The stigma of leading the Kolkata Knight Riders to last in the 2009 Indian Premier League with coach John Buchanan also remains.
However, the word from the dressing room is that he has galvanised some of the younger players. Mitchell McClenaghan (four wickets for 20 on debut at Paarl) and Kane Williamson (145 not out off 136 balls at Kimberley) were examples.
NZC director of cricket Buchanan says McCullum appears to have made progress in the past fortnight.
"One of the things Brendon instils in players is a potential to believe in themselves. He bounces back quickly from disappointment. I think his communication skills are still a big strength. We [New Zealand] need leaders capable of maintaining confidence in themselves and those around them with just 50 overs to work with.
"A lot of credit has to go to the captain, especially in the second match, when they defended a gettable total [280] in the field, especially with the score at 167 for one in the 31st over.
"They turned things around through solid bowling and excellent fielding . There was a visible camaraderie. At times, you can choose to be more defensive in 50-over matches but Brendon's tendency is to give himself every chance of taking wickets. He even leaves a slip in wherever possible.
"That's part of the reason I installed Brendon as captain at Kolkata. He likes to lead by example. I know we faced adversity back then [losing 10 of 14] but he tried everything he could to win those games and it affected his own game."
Ken Rutherford led New Zealand to South Africa in 1994-95 when they lost the test series 2-1 on what became known as the 'sex, drugs and rock 'n' roll' tour. He also witnessed the strength of the South African system first-hand when he returned to play for Gauteng from 1995 to 2000. He captained them to the provincial four-day championship in his final season. Rutherford says New Zealand's one-day series win is still significant.
"It is an intimidating environment and these last few results have finally earned us some respect. A lot of my friends over here [Rutherford works at the South African betting agency Phumelela] have been very quiet in the last couple of days after being quite vocal through the test series. McCullum and the coaching team deserve some kudos.
"I think Brendon's done well. He seems a natural guy for the captaincy, he's made some astute field placements and bowling changes purely because he can see how the game is unfolding with a bird's eye view behind the stumps.
"He's also been selfless with his own batting position, sending Grant Elliott in to score runs [48] at No 4 in the second match. I got the feeling they're forming a reasonable nucleus of a [ODI] side. For example, I'd argue Williamson's century is one of the greatest New Zealand 50-over innings of all time.
"A lot has been made of South Africa playing a lesser team without the likes of Jacques Kallis, Hashim Amla, AB de Villiers and Dale Steyn in each match but New Zealand has fielded a weaker team too, without Ross Taylor, Tim Southee or Jesse Ryder."
Former New Zealand coach David Trist spent time in South Africa during the 1980s, coaching what was then known as Eastern Province to the Currie Cup title. He says McCullum has made the most of a daunting situation.
"Not only were they playing in the challenging cricketing environment of South Africa but New Zealand teams have created a litany of divisions over the years, often caused by outside influences and they can have a negative influence on how we play the game.
"Brendon has been able to put those dramas to one side, most of which were not of his own making, and harness some solid performances.
"I think he has the type of personality which could assist and link a young team together. A number of players seemed to support him and improved their self-esteem in the process."
