Denied Boarding Compensation is covered in Rule 245AS of Alaska's Contract of Carriage. [Click the link and scroll down a ways to find it]:

http://www.alaskaair.com/www2/compan...c_section6.asp

Mileage Tickets are not exempt from being paid denied boarding compensation, but the compensation isn't much. Reading the rule, the minimum is either $37.50 US or $75.00 US depending on circumstances. That assumes the passenger met the check in requirements and that the passenger wasn't put on alternate transportation that met certain time limits.

There are several weasel clauses that allow AS (or other airlines) to escape paying compensation, including:

the passenger will not be eligible for compensation if the flight on which he/she holds confirmed reserved space is unable to accommodate him/her because of government requisition of space