Not sure where to put this, but a few people (including myself) have been a little confused as to a few aspects of these units. In particular, Zhadsnark's "no Big Guns and Kans" rule and how exactly one takes a Mekka Dread in a Codex: Orks army. I emailed Forgeworld with these questions a month or so ago and finally heard back.
Hi,
Thank you for your email and please accept our apologies for the delay in replying to it. If he is the Warlord of the army, then you can't take the Deff Dread, Killa Kans, etc at all. However, if he is not the Warlord of your army, then you can take Deff Dreads etc.
The Meka Dread is Heavy Support.
If there is anything further we can do to assist you, or if you have any queries about the information we have requested or provided, please telephone us.
Regards,
Forge World
So there you go. If he's not the warlord he doesn't apply his restrictions, and we simply take the Mekka Dread as Heavy Support