I did it last strat...Shik attacked an Astralis village, and the next day Remnant (who Shik was a member of) declared they were neutral in the war between Hospitaller and friends vs Chaos/TKoV and friends.
I said that's fine, I'm not going to war with Remnant (unless they want to take it as an act of war) but I was attacking Shik to reclaim the equipment from his plundering the village, and as retribution for his crimes against the village. I rp'ed that I was attempting to arrest him.
However, if someone were to attack a member of the Knights Hospitaller, it would most likely be taken as an act of war against the whole faction.