It's not a Photo Mechanic issue, since PM is just displaying the embedded jpeg that was made in-camera.
Adobe and Nikon software (including the in-camera jpeg engine) are obviously different, Nikon (and most, if not all, camera makers) do not disclose their rendering engine to third parties.
You can get more similar colours to Nikon's rendering if you use Camera Standard profile inside ACR, set the in-camera contrast etc to defaults and disable any proprietary in-camera techniques like D-lighting (which applies only to jpegs anyway, and you are working with raws). Or use Nikon's software to process the files.