"house" just means the yeast they use, it might be from white labs, wyeast, wehenstephan, fermentis etc or it might not. Proprietary means it is their intellectual property. Pacman is proprietary but Wyeast maintains the culture as a service to Rogue and Rogue allows them to market it to homebrewers. Some breweries, generally large ones, maintain their own culture (maybe with a backup at a local hospital in cryogenic storage with redundant power back up).
A lot of breweries will tell you what yeast they use if it is a stock strain from a vendor. If it isn't they should at least tell you if you can culture it from a bottle (ie it is bottled with the primary strain, not pasteurized and not sterile filtered). Some breweries, usually small ones or pubs, will give you a growler full of yeast if you ask nice and swing buy while they are brewing.