No, it is NOT legal in WA!
I doubt it's legal in OR either. Even in CA where lane splitting is tolerated, they don't allow you to use the shoulder. In WA, if there happens to be a LEO in the traffic and you pass on the shoulder, it's a fast way to a big ticket! If you pass more than three cars the officer can write you up for reckless driving... and the fine for that isn't cheap. Add on the big hike in your insurance that'll go with it and you'll be wishin' you would've just waited in the traffic.