You can actually fill your CAD (normal force org) or Ork Horde Detachment (3 hq 9 troop faq) with selections from any Ork Faction. So if Ghaz supplement has new unit types (and is Ork Faction, not its own faction) you could slot them into normal force org slots to fill a CAD. The same for Forge-world army lists if they are ork faction.
I don't think these books specifically are this way, at the moment, however.... I think the Ghaz supplement is mostly just formations...
But, to try and reiterate for clarity. In a CAD formation, if we had 2 or 3 books that are all deemed Ork Faction, you could pick 1 HQ from the Codex Orks, 1 HQ from the Ghaz supplement, 2 Troops from Codex, a Heavy Support of a Tank from the Deffmob (IA8), a Looted Wagon as a Heavy support from the White Dwarf, and a Heavy support of Lootas from the Codex. And then still take a Formation from any Faction source.
(Or you could even take a Tau or Tyranid formation if you wanted... those models would just be restricted by ally type - desperate allies or come the Apocalypse allies...)
As long as the selections are from the same faction, you can fill the force org from any source. It makes tracking rules a pain, if supplements have their own army wide rules (e.g. imperial fists from SM and from their supplement)
Am I right? Does that make sense? Correct me/clarify me if not
-rhuntar