The white rhino was saved due to the efforts of a few visionaries who convinced the South African government and Swaziland, if I recall correctly, to allow the commercial breeding of white rhino (which means for profit, in case you don't understand economics 101). The fact that people, including Mericuns, could hunt them for large sums of money, meant that there was money to protect them and breed them. That's what saved them
The timing simply doesn't support this theory as sole or primary driver--the hunting program wasn't launched until 1968. By then conservation measures had already resulted in a tenfold increase in the white rhino population from their turn-of-the-century lows.