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Yes, although all CD <ALLEGIANCE> units must align with the same god.

Edit: Above info is wrong The only exceptions to this are as follows:
The <MARK OF CHAOS> and <ALLEGIANCE> keywords - these can be different for different units in a player’s army.
The DREADBLADE and FREEBLADE keywords - these units can have different selectable Faction keywords to other units in a player’s army.
SPECIALIST MOB units.

 Dysartes wrote:
Question - is CHAOS a sufficient keyword for the detachments between two books to be Battle-Forged, or would the OP need to use SLAANESH as the linking keyword?

It's sufficient for the overall army, but not for the individual detachments in the army. You cannot for example have Noise Marines and Bloodletters in the same detachment, but you can have them in the same army in different detachments.