Warner received a 12-month ban from Cricket Australia for his role in the ball-tampering scandal that marred his country's Test series in South Africa earlier this year.
His suspension extends to state cricket, but the opener is free to represent Randwick when the Sydney grade season begins.
Former Australia bowler Whitney was quoted as telling the Southern Courier: "We're delighted to have him [Warner].
"He's one of the best players Australia has had since World War Two. He's been speaking to one of our club officials and he has committed to the first three or four rounds of the season.
"Why it is only three or four rounds at this stage, I don't know. Everyone is excited to have him. He will be great in the changing rooms with younger players."
Earlier this week, Cameron Bancroft - another player banned for his part in the ball-tampering incident - was cleared to play grade cricket in Western Australia.