I recently flew an S fare NRT-SFO-NYC (a special two US city fare from Japan available only online). I got mileage and status credit for it, though looking back at my mileage history just now, I see they credited it as a K-Class flight (whatever K class is--it's not SWU-upgradable, just as S is not upgradable).

In fact, they like to credit things as K-class a lot. I also just noticed that they credited the first leg of my SFO-LAX-NRT-BKK W-class ticket as K-Class (and my upgraded LAX-NRT as C class). (I'm mid-trip right now.)