Wow this is a pretty magical track. Very dreamy and space-like with all that chanting that seems to be a trademark with the Atreides soundtrack.
I'm not quite sure who the Overseer actually is with respect to the title of the track although usually different houses are made responsible for overseeing the harvesting of spice from the planet Arrakis. According to the Dune wiki these planetary fiefs or siridars were handed down by the Padishah Emperors to Great Houses. The planetary governor would be responsible for submitting tithes to the Emperor after collecting profit and taxes from the populace of those living within the fief. Apparently these fiefs could last for thousands of years (a pretty long time) but the Emperor could just as easily withdraw a fief from a Great House. The planet Arrakis was a siridar fief of the Imperium and whichever Great House has possession of it would usually maintain a large population from their own homeworld.