There had been speculation that Olivier might have to sit out at Newlands because of the return to fitness of Vernon Philander. But Du Plessis said he would definitely play.
"He brings variety to our attack," said Du Plessis.
"Duanne is more of an enforcer who puts you on the back foot and can be a bit challenging for batters, especially when they come from the sub-continent where the ball doesn’t bounce as high," said Du Plessis.
"He’s a fit guy and he can bowl long spells. He’s different, he runs at you, he’s around your head most of the time, it’s not comfortable."
Pakistan captain Sarfraz Ahmed acknowledged that Olivier had caused problems for his batsmen in Centurion.
"We will definitely talk about him. He’s a different type of bowler with a fast bowling action," he said.
Du Plessis said South Africa did not want to let Pakistan off the hook following their collapse in the second innings in Centurion.
"You could see there were one or two things in their batting line-up that we could get through. For me it’s about making sure we keep that pressure on them," he said.
Sarfraz said Haris Sohail had not recovered from a knee injury that kept him out of the first Test and was unlikely to play again in the series. He said Pakistan would keep the same batting line-up that played in Centurion.
Sarfraz admitted there were big challenges for his batsmen on fast, bouncy pitches. "We are used to playing on low bouncing pitches. But our players are good enough and they have been working hard in the nets and talking to the batting coach."
Du Plessis said the Newlands pitch looked similar to those used in recent years, with help for the fast bowlers and the possibility of taking spin later in the match. A Test against India last January was completely in what was effectively three days of cricket.
He admitted that bowler-friendly conditions were difficult for South Africa’s batsmen as well as those of the visitors.
"Our success rate in home conditions in the last three years has been very high," he said. "It’s been tough on the batters when you’re playing against quality seam attacks, which most teams have these days. But we’re looking to play winning cricket. Our focus is to win as many matches as we can."
Sarfraz said the return of Mohammad Abbas to the bowling line-up would strengthen his team, while he expected the pitch to have "something" for leg-spinner Yasir Shah. "Our bowling gives us so much confidence," he said.