ok we all know there are some some legions out there who make wide use of daemons in their battles (word bearers, black legion) but what i was wondering is what happens between battles, I ask because ive just gave the girl friend 4k points worth of death guard and a chaos fleet for BFG and was wondering how they would interact with my 3k nurgle daemon force?

is there any established fluff out there saying daemons can be found on chaos ships or are they just summoned as needed?