I don't quite think the OW formations are as fitting. A very low magnitude of your stock cultist or ganger is enough to present some potential damage to the acolytes, while still fitting in with the main themative elements of Dark Heresy.
The acolytes are, by the virtue of their profession, get themselves stuck into the middle of very dangerous events occuring. There will be cults, gangs, organizations, all with their own bases, lairs or meeting places. Acolytes arriving in the center of these vipers nests should tread carefully - relying on stealth, the wit of their tongue, or when pressed - their combat abilities to see them through the day.
I personally believe this shouldn't be so easy to the point that it's simply brushed away narratively. My own experiences with using the horde rules, generally setting a small cult or gang to magnitude 2-5, is enough to push some pressure on my acolytes while ensuring they don't get too bold or gung-hoey.
Lastly, I don't really buy the 'it's film noir, not badass action'. That's down to the to gm, the players, and each individual scenario we devise. Dark Heresy's strength is based on the Warhammer 40k setting, which envelops everything from murder-mystery to outright planetary wars, to epic confrontations between the forces of order against chaos. Eldritch horrors, petty gangers, and miscommunication between allies all make for trappings from any conceivable genre we wish to utilize.