Good question. Pretty sure it used to. But I recently booked a mixed cabin JL(J)-AS(Y) award through AA, and while I was able to select a seat in PC (actually I found I was already pre-assigned one by the time I brought up the reservation on AS website), there was no message that I was waitlisted for First like I am used to seeing on a paid reservation. Instead there was a message saying that I was Upgraded to Premium Class, even though I should have access to those seats anyways.

Anyways, might want to ask on the AA forum. I was going to post there until a better routing opened up soon afterwards that didn't require an AS segment in Y.

Complimentary Upgrades on Alaska Airlines (AS)