"But we're unlikely to need a third spinner in South Africa, which is why we've opted for another seamer in Doug."
Hesson said the absence of four front-liners meant new opportunities for several players.
"There are chances there for batsmen such as Tom and Colin, for Ish and for a handful of bowlers," he said.
"And, not least, it's another good opportunity for (stand-in captain) Kane Williamson to continue upskilling in terms of leadership."
The tour starts with the opening ODI against Zimbabwe in Harare on August 2.
New Zealand team to tour Zimbabwe and South Africa next month:
Kane Williamson (c), Martin Guptill,Tom Latham, Ross Taylor, Grant Elliott, Colin Munro, Luke Ronchi, Jimmy Neesham, Mitchell Santner, Nathan McCullum, Ish Sodhi (Zimbabwe only), Doug Bracewell (South Africa only), Mitch McClenaghan, Ben Wheeler, Adam Milne, Matt Henry.