They don't track when you enter your room for privacy reasons, otherwise housekeeping would know when you are there and when you aren't and could make sure they only come when you aren't.
And you assume that people always pass through the guard shack or use DME. Security will waive Taxis, Minnie Vans and several other types of vehicles through, especially if there is a backup of traffic.
So it would be virtually impossible for Disney to tell if a room isn't being used, except when housekeeping enters and sees no luggage, beds still made, etc.