Six-time IndyCar champion Dixon reprises his role as third driver for Ganassi's #01 Cadillac DPi-V.R alongside full-season pairing Sebastien Bourdais and Renger van der Zande for the Road Atlanta classic on October 1.
Hunter-Reay meanwhile will share the #02 Caddy with that car's regular drivers Alex Lynn and Earl Bamber.
For Dixon, it will mark his first IMSA outing since the Rolex 24 at Daytona in January, as he was forced to miss the Mobil 1 Twelve Hours of Sebring in March due to a clash with the Texas IndyCar round.
Hunter-Reay joined Bourdais and van der Zande for the Sebring race but now switches over to the sister car for what will be his first Petit Le Mans appearance since 2020.
The two Ganassi cars are part of a seven-strong top-class entry for what will be the final race of the DPi era at Road Atlanta.
As expected, Loic Duval (JDC-Miller MotorSports) and Mike Conway (Action Express Racing) will be present as respective third drivers for their teams, while AXR's second Cadillac returns with Mike Rockenfeller, Jimmie Johnson and Kamui Kobayashi again sharing driving duties.
In the Acura camp, Wayne Taylor Racing had already announced Brendon Hartley as its third driver for the title decider, and Helio Castroneves will be back in the Meyer Shank Racing ARX-05 for the first time since Daytona.
A 48-car entry list is completed by seven LMP2s, 11 LMP3s, seven GTD Pro entries and a bumper crop of 16 GTD machines.
Ex-Mazda racer Tristan Nunez will make his second outing with LMP2 squad PR1/Mathiasen Motorsports after joining the line-up for the #11 car at Road America in August. He will race alongside Josh Pierson and Steven Thomas.
Indy Lights driver Christian Rasmussen is a new addition to the #18 Era Motorsports line-up alongside regulars Kyle Tilley and Ryan Dalziel.
In GTD Pro, Jesse Krohn is back with BMW Team RLL for the first time since Daytona, with Augusto Farfus instead expected to race in the clashing GT World Challenge Europe Endurance Cup finale in Barcelona.
Tom Gamble joins Ross Gunn and Alex Riberas in Heart of Racing's GTD Pro entry in an effective swap with Maxime Martin, who remains in the Aston Martin outfit's GTD car with Roman de Angelis and Ian James.
Previously announced third drivers Nicky Catsburg (Corvette Racing), Felipe Nasr (Pfaff Motorsports Porsche) and Kyle Kirkwood (Vasser-Sullivan Lexus) are back with their usual respective teams in GTD Pro.
In GTD, Alessio Rovera returns to Michelin Endurance Cup-only Ferrari squad Cetilar Racing for the first time since Daytona, while Seb Priaulx is a new addition to the Inception Racing McLaren team.
Track action for the 25th running of Petit Le Mans begins on Thursday September 29 at 9.50am Eastern Time with first practice.