Combined Arms Detachment confusion. (Don't want to be Unbound.)

[Sotane]

I'd rather find this out now before I spend some money. If Orks are my Primary Detachment (Such as the Green Tide) can I take Elder (Desperate Allies) as a combined arms detachment and still be a bound army. (I'd rather not chuck money at this just to end up with an Unbound army list if that's the case.)

[Charon]

Yes. As long as everything either fits in a detachment or Formation, you are bound.