I'm sure you can get in when flying AS metal and that if you are on AS metal it makes no difference what airline code is on it. The question is - what about if you are flying NW or Delta metal on a NW or Delta coded ticket? The NW web site seems to indicate that you'll be admitted, but I didn't think that was the case.
I think the NW web site forgot to mention that if you are flying Delta or NW metal, it must be an Alaska coded ticket.