Ok, I did some more digging around and it does appear that a dependent with valid ID can purchase the companion tickets without the active duty member being present (this allows families of deployed service members to still take advantage of the offer.) This is from the official press release about the deal:
"Disney’s Armed Forces Salute Companion" tickets for family members and friends may be purchased only by active or retired U.S. military personnel, including activated members of the National Guard or Reservists (with orders showing active status after Jan. 1, 2008) and active or
retired members of the United States Coast Guard (or, in each case, their spouses, but not both).
• Military personnel (or their spouses) who purchase "Disney’s Armed Forces Salute Companion” tickets for admission to the Walt Disney World Resort for family members and friends will need to activate those tickets at Main Entrance theme park ticket windows in order for those tickets to
be used (regardless of where those tickets are purchased).
• Military personnel (or their spouses) who purchase "Disney’s Armed Forces Salute Companion” tickets for admission to the Disneyland Resort for family members and friends will receive exchange certificates to be redeemed by such military personnel (or their spouses) for tickets at Main Entrance theme park ticket windows (one ticket per exchange certificate)
.
• The military personnel (or spouse) will be required to present valid military identification (which, for activated members of the National Guard or Reservists, also includes orders showing active status after Jan. 1, 2008) for all ticket transactions (including to activate tickets, and/or redeem
exchange certificates for tickets, at Main Entrance theme park ticket windows). A valid ID may also be required for admission.
• "Disney’s Armed Forces Salute Companion” tickets are limited to five per service member (regardless of place of purchase and whether purchased by service member or spouse) and all five must be purchased at the same time. Accordingly, no service member (or spouse) will be permitted to activate, and/or to redeem exchange certificates for, more than a total of five "Disney’s Armed Forces Salute Companion" tickets for the Walt Disney World or Disneyland Resort (regardless of whether activated or exchanged by the service member or spouse).
Hope that clears some things up. The complimentary ticket, of course, is only good for the actual service member.