Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

So in the old IG FAQ this question was asked: Q: Can Ministorum Priests or Techpriest Enginseers be taken as the mandatory HQ choice? (p93)

And was given this for the answer: A: Yes.

Since 6th edition however, this was apparently changed to this: A: No. You will need to take another model to be your Warlord

So that's great for Imperial Guard players. Nice clear answer there. But what about the rest of us taking Imperial Guard as allies? The IG HQ can never be the Warlord, so does this ruling apply? Or does the previous FAQ answer still apply in 6th Edition?

As far as I can tell, you should be able to take a Ministorum Priest or Techpriest Enginseer as the Allied Detachment's mandatory HQ. With regards to the FOC and how it works, nothing has changed between 5th and 6th edition. The only thing that would be applicable would be the rules for the Warlord, but since Allied Detachment HQs can never be Warlords there doesn't seem to be a restriction on the Allied Detachment.

What do you guys think?

He doesn't take up a slot, so he doesn't fill a slot.
So the mandatory HQ slot isn't filled.

IG p93 seems pretty clear

"XXX do not use up and Force Organization chart selections, but are otherwise treated as separate HQ selections."

A better question might be, can an IG Allied detachment still take Ministorum Priests and/or Techpriest Engineers at all?

They cannot be taken as the mandatory HQ slot as GW said so. However, since they do not fill a slot, they can still be taken in an allied detachment.