Yes. After you purchase the ticket (but not until then), the reservation on Alaska's web site will say "your Delta elite status has been confirmed. There may be new seats available to you, click change seats idea the updated seat maps." On 737s, row 6 are the best seats (extra legroom but not an exit row), followed by the exit rows (row number varies by 737 variant).
If your companion is on the same reservation, you'll both be able to select priority seats. If not, call 800-ALASKAAIR and ask to put the companion in the priority seats. Also note that the reservation page on alaskaair.com has a "link reservations" link which can be used either for a travel companion on a separate reservation or for your own connecting flights on a separate reservation, though you still have to call for a companion's preferred seating.
Note that this delay is less annoying than Delta. With Delta, I can't select preferred seats until after ticketing. With Alaska, I only have to wait until purchase.