There is no prohibition on Mediators referencing one or more Proxies. Most demos show one of the Mediator's onRegister responsibilities as retrieving references to frequently accessed Proxies.
The classic MVC meta-pattern diagram shows that the View may update the Model directly. Updates do not have to go through the Controller region, though they certainly may.
Here's a brief refresher:
http://puremvc.tv/#P100/T110-=Cliff>