You can do that, but you may be better off just transferring the SPG points to Alaska Air if you plan to fly coach, depending on when you are taking your trip.
AA has peak and off-peak SAAver awards for Hawaii. Off-peak is 17,500 OW and peak is 22,500 OW. Off-peak season for Hawaii is Jan. 12 - Mar. 8; Aug. 22 - Dec. 15. Alaska is 20,000 OW all year for super-save coach. If you plan to travel during off-peak season, move the miles to AA; if you plan to travel during peak season, move the miles to AS. -- Suzanne