Because the field of the pickup is so small, the likelihood
of interferance by another field from an alternator -
unless it was placed within a few millimeters of the
pickup - is really, really small.

        The stray field from a PM Alternator rotor would likely be a problem for the pip sensor.  If the alternator were carefully designed, the stray fields could be minimized, but I wouldn't bet my life on it. Would you?

        I would move the alternator or the sensor to the flywheel end of the engine.

   Look up "Hall effect".

        The RX-8 sensor appears to be a coil type, (like most crank angle sensors,) rather than a Hall effect type.