@Caramon well the Inquisition is dealing with more internal politics and kind of like the inquisition of the Spanish in old times. While Marauder are those that go out to help conquer worlds for the Sith. From my understanding Inquisitor is internal dealings, while Marauder are those that fight the external threats
Besides what they said, marauders are your average sith, while the ones of the inquisition are more faithful to it, they use their faith instead of anger and that stuff, so, they are the religious ones.