They extend benefits such as priority boarding and free checked bags, but not upgrades:
http://www.aa.com/i18n/utility/EliteAS.jsp
I can't find it published anywhere, but I don't believe Delta Silver Medallions receive complimentary upgrades on Alaska, either. Pretty sure that benefit is only for Gold Medallions and above.
In any case, I'd rather have AAdvantage miles than SkyMiles!