In a delted scene, Michael sends Neri to oust Klingman from his hotel. After Klingman caves, Neri sits down and orders the showgirls to resume their rehearsal. That tells me Michael may have given Neri a piece of the hotel.
That's mere speculation. Fact is that Neri was put in charge of security of the Las Vegas hotels, effectively being in charge of those hotels.
Also, as a response to your other arguments, Neri was unofficially acting as Michael's underboss, while Fredo formally held that title. Obviously Michael prefered Neri above Rocco, as he himself had chosen Neri as his personal enforcer, while Rocco was introduced into the organization by Clemenza.
