According to various sources, it's gonna happen. Former 49ers head coach will be the Packers new defensive coordinator.
Although Nolan's recent teams in San Francisco and Baltimore (as defensive coordinator from 2002-2004) ran a 3-4 defense, they would probably keep the 4-3 scheme because the current roster is better suited to it:
“He’s good now. He’s smart,” said the scout who’s familiar with Nolan. “He can run 3-4, 4-3, he knows it all. It depends on what personnel you have. He’ll do whatever, morph to whatever. He’ll use your players to their strengths. He’s smart that way.”