IGN confirmed it in a trailer analysis video. Well, they confirmed that Cullen is head of the military division anyway.
I watched that just a short while ago and I couldn't tell if they'd received 'confirmation' from an actual Bioware source, or from just reading the forums.
On some issues they clearly knew things from speaking to Bioware devs (like multiple mounts) but in other areas they were just totally wrong, like saying Nevarra and the Free Marches were locations in the game.
That said, a lot of other evidence suggests that those three characters are heads of different parts of the Inquisition, including the fact that they were the only characters pictured in the new War Room table art without weapons.
I do think that Scribe Lady is going to deal with diplomacy as well as commerce and trade, since that seems to be another area in which the Inquisition has interests and can influence the world.