[X] Yes.
-[X] "I have been told of your history. That your people overthrew a feared tyrant. The people of Barbarus have as well. The more I was told of the Dusk Raiders, the more parallels I heard with those who'd fought beside me. I find this promising. The Emperor made a promise to me, that there were more monsters in the galaxy like those we'd already vanquished, which I would fight. Will you kill them with me?"
Blunt and to the point regarding Mortarion's goals, which at this point are basically just "the Emperor seems somewhat trustworthy, but the most important thing is that there's more Overlords in the stars." I like this.