Diamond magnetometers might not be a great fit for this application. They require a powerful laser, RF, and are presently huge and impractical. Also, they are just terrible at accuracy and drift like crazy. Finally - and this is the thing I really can't get - they require a giant magnetic field to operate. If your magnetometer has a giant magnet bolted to it, you would expect it to basically measure drift in that magnet. Diamond magnetometer people will jump out of the woodwork now, but I haven't seen published high quality data that says otherwise. Would love to be proved wrong.
Diamond magnetometers are great at being a magnetic microscope since they have really high density of measurement sites and you can stick it right up next to an object of interest.