Yeah on my 2000 the cargo area light definitely goes on when you open the hatch door. Over the weekend I forgot to shut the hatch after unloading some stuff and the light was on all afternoon
Not sure where the sensor is sorry.
Edit, wait a second, so you're asking if the regular interior light goes on if all you do is open the hatch (and not the doors)? No I don't think that light is supposed to go on if all you do is open the rear hatch.