Join Date: Jul 2012
Location: Mississauga, Canada
Coteaz can only be used via an Inquisitorial Detachment, and does not count as the HQ selection for your Combined Arms/Allied Detachment of Guard. You're still looking at 1 HQ and 2 Troops for Guard with the options you're familiar with, and then 1 compulsory HQ with one more optional and 3 (I want to say) optional Elites selections for the Inquisitorial Detachment.
The Inq. Detachment can be your Primary one and Coteaz can be the Warlord, but you still will need a valid HQ option from the AM 'dex.