Technically, though, there's no legal ground for the Ordo Hereticus to pursue a war against a Rogue Trader harboring a renegade space marine, since he has the authority to do so outside the Imperium.  Now, if such an individual were to be operating within the Imperium for an indefinite period...<br/><br/>(Outside the Imperium, which covers every part of the Mextil cluster outside the Ares system, Rogue Traders have authority equal to the Emperor himself, though they have to enforce it themselves.  Coincidentally, the Speak Not Unto the Alien trait also doesn't apply in the Mextil Cluster outside the Ares system, since people in the Mextil cluster live side by side with xenos without hating or killing them.)