I used the idea that Chaos and The Hive are natural enemies in my campaign. It seems logical to me; they both have the same prey, the Hive will eat just about anything that gets in its way, and the Shadow of the Warp has a deleterious affect on Warp users. The main thing might be that Chaos would prefer not to fight an enemy they literally get nothing from (no souls, no slaves, no tech etc).
I set the campain on Castobel (before the recent official source material books were released) and used Inquisitor Quist (Quint?) as the one with the theory. She believed that the self-destruction of one of the Hives on Castobel was not suicide, but rather a mass sacrifice from Chaos cultists or even Traitor Legions as a strike against the Hive. She had evidence that a ship aligned with the Stigmartus had gotten through the blockades around Castobel, 48 hours later the Hive City exploded when its reactors were purposefully overloaded. The majority believe it was an act of suicide, but she believed that the chaos forces caused it. For my purposes the explosion was more of a neutron bomb, leaving most of the city intact.
The PCs were dropped in Castobel and charged with investigating and setting up a base for the Inquisitor. They walked right into a war between genestealer cults and chaos cults, both being whipped into frenzies by their respective patrons. Once the base was set they investigated various leads, put out some fires (a small chaos space marine warband) and verified that it was indeed an attack from chaos that destroyed the city, a massive sacrifice with the power to be used to summon a Daemon Prince and his armies. They believed a chaos sorceror and a newly made chaos space marine named Guillaume were the orchestrators, with the newbie CSM to be possessed by the Daemon Prince.
The PCs decided to try and lure the tyranids into the ruined city, the Inquisitor's Acolytes were already looking for a Psyker that had touched the mind of the Hive and was still on the loose. They would capture him and since he had an effect like a Pied Piper to the Tyranids, would lure them right into a dead city where the radiation would kill plenty before too long. The PCs were going to enter the city and see if they could stop the ritual, and if they couldn't they'd at least make certain that the daemons and tyranids fought.
Daemons were already popping up in the city, but they found where the ritual was being held, the sorceror though was behind a field and couldn't be hit, while the Acolytes were flying a damaged ship into the city and leading a whole mess of tyranids with them; they had the psyker.
When it seemed that the ritual was about to go off suddenly the would-be sacrifice pulls his gun on the sorceror.
"Guillaume? What are you doing? You have to enter the circle!" the sorceror said.
"I am not Guillaume. My name is Alpharius." he said before blowing the sorceror's head off and then fleeing the scene. (I loved that part in Tales of Heresy on the Worldeater ship when two Alpha Legions revealed themselves)
From there, without a sacrifice, portals to the Warp opened and Daemons poured in, just as the Tyranids arrived en masse. The PCs thought it best to chase after the fleeing Alpha Legion and let those two groups sort it out. They chased after the fleeing CSM, who was then killed by a Zoanthrope and some of the Tyranid Warriors. The PCs killed them and made it out of the city. When they contacted the Inquisitor they found that the last remnants of the Genestealers and their cults had attacked their base, and only she, some of her Acolytes and a few local guards survived. While she was speaking, two of those suddenly turned on her saying they too were Alpharius, and killed her.
The PCs were the heroes of Castobel…and quite confused at the end of it all. But they liked the adventure. I had a good time running it also.