I've run two major campaigns in the OTU... one was far away from it, but in the same universe (an isolated group of humans dropped far away from the Imperium by the Ancients). The other was based on Glisten during the 5FW. That let me use all the 5FW material in JTAS and the books, but we weren't on the front lines.
I took the Zhodani stuff from Leviathan, and speculated that since the fleets were busy elsewhere, the "war" in Glisten, District 268, 5 Sisters, and the rimward subsectors of Trojan Reach operated more like an extremely violent tradewar, with the occasional TL 11 Swordy big ship to stir things up, and a huge Impy presence in the 5 Sisters that wasn't going to leave it. Fun merchant/paramilitary stuff, all done with ships under 2000 tons. Lots of "privateering".
But I agree with Hans and Rob. It's about how much you want to have to work on it... the more "official" stuff you use, the less you have to do yourself.