Back EMF is great for sensing the position of a spinning brushless motor. This is important because you must switch the coils being driven in close synchronisation with the position of the motor.
It doesn't work on a stationary motor. For brushless motors which must start smoothly from standstill, usually hall-effect sensors are added.
You may be able to measure the current going to the servos to identify which servos are using a lot of power to maintain their position. This is a pretty crude measurement, nothing like a sense of touch or pain.