Gatland named a 37-man touring squad with Welshman Alun Wyn Jones as captain. The Springboks are expected to announce their squad early next month.
“The announcement of the Lions squad was a marker in the ground in terms of international rugby coming back to South Africa, which is phenomenal for us, because we’ve been out of it for a while,” Nienaber said in reaction to the big announcement.
Gatland has, during his long stint as coach of Wales, managed to build a successful track record with the Welsh Dragons against South Africa in the past few years with a specific style of play.
“One thing I do know about Warren is that he will do his homework," added Nienaber.
"If your look into the past, the Welsh were a team that we always struggled against. We had one win (against them) since the 2015 RWC quarter-final, which was the 2019 RWC semi-final in Japan."
Under the guidance of Gatland, the British & Irish Lions defeated the Wallabies in Australia in 2013, and four years later they managed to draw their three-match series with the All Blacks in New Zealand.
With the British & Irish Lions squad now revealed, the attention shifts to the coming Springbok squad selection.
Locally, the franchise teams started the PRO14 Rainbow Cup SA on a high note last week, making for some extra spice knowing that there are Springbok places up for grabs.
"If you look at the last weekend’s Rainbow Cup action then you will see that the intensity went up a notch," said Nienaber.
"I must say we have a nice relationships with our franchises, allowing us to meet the players just to align ourselves again.
"And the pleasing thing for me was to see how the players are working on and improving on the things we spoke about during those alignment camps.
"I think we have less than 80 days before we play the Lions and the coaches and players have to utilize every second of that time to make sure we are well prepared for the Series."
Looking forward to the three-Test series against Gatland and his team, Nienaber said: “The Lions series is a special occasion that might come only come once during the career of a professional rugby player.
"I know for a fact there are certain players who have postponed their retirement because the tour was two years down the horizon. So I think all the stars are aligned for a great series."