It depends upon a number of things: the size of the winery, the time of year, how busy is the tasting room, whether the winemaker is present or not.
For some of the smaller Oregon wineries, the winemakers both produce the wine, and run the tasting room. If you are at a tasting room, and would like to speak with the winemaker, it couldn’t hurt to ask. The winemaker may be on site. If the winemaker is not available for comment, however, just remember they are extremely busy all year round, producing the great wine you are tasting!