I'm not sure I understand what this poster is trying to say,
CAD's don't have 'ally slots', nor does anything...
Anyway, back to the
OP - Without knowing much about the Daemons Codex, I presume Karanak is a special
HQ character?
Basically, you've got a
CAD (Combined Arms Detachment) of Chaos Space Marines, containing two
HQ's (Belakor, who can be taken for either
CSM or Daemons, and a Daemon Prince), two Troops (the Cultists) and three Fast Attack (the Heldrakes). So far, so good, perfectly legal.
Next you've got two separate Allied Detachments, each with a
HQ (
LoC / Karanak?), a Troop (I presume Nurglings are Troops?) and a
FA in one (the Hounds). Again, legal, but there is another way of doing it - just take another
CAD for the Daemons and lump them all in together (leaving you with a
CAD of
CSM, and a
CAD of Daemons).
Some tournaments don't allow double-
CAD, but it's allowed by the main rules. You can take any combination of detachments in a Battle-forged army.