How much info do you think Rogue Traders have about the Horus Heresy? I am working on an adventure now where a group of pre-heresy Luna Wolves have been shot out of a warp storm 50 years ago. The wolves ship was damaged in a warp storm and can no longer travel warp space. The wolves land on a planet and over the course of the 50 year period proceed to "bring the planet back into the imperial fold."

Flash forward to present time and the explorers exit warp space to take a navagational fix and discoverthe planet, newly emerging from the warp storm that had surrounded it for the last 12,000 years.

So the explorers land and discover the Luna Wolves, but how much would they know about them given the nature of the heresy and it being so classified?

The kicker is most of my players know very little lore, so they wont know much about the heresy themselves.

Rough details are known, since as you said, a lot of it is covered up. You'd probably have to have Forbidden Lore (Heresy) to know the details, and if the Marines still refer to themselves as the Luna Wolves (remember that they had their name changed before the Heresy to the Sons of Horus) then the Rogue Trader probably wouldn't know the difference between them and any other Marines, since it's unlikely that the Rogue Trader will have ever seen a Marine before, 99.9% of people in the Imperium never have.

If they call themselves the Sons of Horus though, even if they don't think they're from the original Traitor Legions, they would at least think they were probably Chaos Marines.

Yeah I want the Wolves to be heroes on the world, having saved the people of the world from some terrible (yet to be determined) fate. The Luna Wolves themselves will have no knowledge of the heresy and will inquiry fairly quickly about the crusade and the well being of their legion, primarch and the imperium.

I think it will be interesting to see how the Explorers handle the situation, of course it will be interesting also to see how the Luna Wolves react to whatever they learn from the players.