Minimum wage in Oregon is $11.25/hr with no special considerations for wait staff. Tips are always on top of the hourly wage and do not subsidize the wage paid by the restaurant.
Having never been to Oregon: the interesting follow up here is, are you as a customer less incentivized to tip with this knowledge? As a Texas resident who has worked in food service in the past, 20% is near obligatory barring subpar service (Texas is one of the states that pays $2.15 an hour for waitstaff).
