It depends on what kind of servo you are talking about. If you are talking about the LEGO motors with built-in encoders, then yes, you could use them as sensors. But if you are talking about servo motors that connect to the Textrix servo controllers, then no, there is no feedback for these motors. Would you describe more details on how you would use two light sensors, an IR beacon and a touch sensor? I can't imagine how you could use those. Out team uses two IR seekers doing triangulation.