Definitely not my area of expertise, but you didn't mention the type of motor before... car or electric.
And the answer would still be different with type of electric motor. Just guessing... (again not my area of expertise) there's DC, AC, Two phase, three phase, and probably a whole lot I don't know. For instance, I'd say...
- electric motors using permanent magnets, and windings on the rotor, I'd say probably not. The main field fluctuations are going on inside the motor between the magnets where you can't get the sensor (easily)
- For those that use stationary coils, and either permanent magnets or coils on the rotor, you might be able to. I would imagine you would need calibration to every type of motor. Because things like the number of coils and two/three phase would change the rotating field considerably. Sounds like a huge science project. Let us know here if you try it and how it goes.