While turning a stepper motor does generate an AC output, it's not suitable for a general position sensor.
The magnitude of signal it generates is proportional to its speed. As long as the table moves at least at at a minimum speed (which will depend on the sensitivity of your measurement hardware), then you will see all the pulses. Move at a lower speed, and you will miss pulses. With a simple voltage measurement, you would not be able to tell whether the motor was stationary, or turning very slowly.
A position sensor really needs the ability to be able to tell stationary from slow. An optical encoder can do this, as can a synchro.
Some constructions of stepper may permit you to sense its position by measuring the inductance of all the windings, treating it as a sort of variable reluctance synchro. However, by the time you've done that, it would be far simpler to use an optical encoder.