I just booked an AS ticket ( via Expedia.ca so I could get it in CAD at par exchange from USD, secret for all you canucks out there ).

I did NOT put in my WP number in Expedia, but I went into 'manage my booking' at Alaskaair and immediately a red message at the top said "your Northwest Airlines Gold Elite status has been confirmed - new seats may now be open and available to you - please click on 'change seats' to view"

Sure enough, I had my pick of the primo seats that I could not get before, and snagged the first row of econo at the F bulkhead on all segments of my flight. This was not a full fare Y.

So YMMV but I WAS able to get preferred seats with my NW status.