Can they duo in QK? I wasn't under the impression they could but the Army sais otherwise. It's not on the wIki list. http://wiki.infinitythegame.com/en/List_of_Fireteams#Qapu_Khalqi If they can, are they 'mercenary'?
I think you're linking N3 content. Answer is no, however, as it's not in the list here: https://assets.infinitythegame.net/downloads/secotrialsn4/all/v1.2/secotrialsn4.zip (You'll note how there's a few more above all else Haris fireteams in the sectorialsn4.zip images)
It's confusing, yes, to have a skill that doesn't do anything, just like it (currently) does nothing in a vanilla faction.
It looks like Scarface and Cordellia can form a Special Fireteam Duo in Druze but not in Ikari or QK (not sure what other factions can take them).Army matches what is in the sectoral fireteam charts for each of those three factions. It seems odd to not be able to take them as a Fireteam Duo everywhere that can take them though.
So can they each Duo with a wildcard or is forming a Duo completely out of the question because the sectoral charts don't show them as having a Duo available for QK or Ikari?
I think there are a few oversights with QK regarding the fireteam charts. In addition to adding a special duo for Scarface and Cordelia, I think Druze should also receive a Haris option, as it shows up in their Haqq Vanilla profile and they have Haris in both Ikari and DBS.