Can I status match to Alaska, use that status to upgrade but still credit the miles to AA?
According to numerous posts by AS staff in the AS forum, no, you're not supposed to do this- you must credit flights to AS if you wish to use your AS elite benefits. In practice, it may not be caught (AS forum posters have said they have successfully done this).
EWR-SEA is one of
the hardest complimentary upgrades in the entire AS system (as a transcon to NYC, lots of people just shell out the $ for F, thus the required "U" fare class isn't available for advance bookings, and F often sells out before anyone gets a free upgrade), meaning that you may blow your one lifetime status match for an upgrade that doesn't happen anyway. Unless you're flying AS more than just the round-trip, you might want to be careful with this.