Yes. All their KeyMount muzzle brakes and flash hiders (unless specified) have a .30 caliber aperture, even the ones for 5.56 (1/2x28 threads). You will need the one with 5/8x24 threads. This was recently answered on DA's Instagram stories. But if you'd like to verify, callsign them and asking never hurts.
Also the KeyMount is the brake or flash hider that mounts to the weapon...Which the KeyMo attaches onto. The KeyMo setup is the mounting adapter system that screws into the suppressor. Just FYI for future reference with the proper nomenclature for each item.
Also all things considered, the .30 Nosler is essentially the same as the .300 WinMag in both velocities, pressures, and performance. So, I'd say he's good to go, but I'd still verify with DA before proceeding, that way he has verification from the manufacturer.