You probably forgot that for a Necromancer, any other Castle is like home; your logic in "Prince of Darkness" disappoints me. :D

Soldier's Luck increases the chance of stunning by Vampire Princes (they, like Lords, often attack without retaliation, and the Princes' stats are higher) and the chance of stunning by Skeleton Warriors. Skeleton Warriors are, of course, quickly destroyed (in your hands, peasant zombie), but you don't have to put them in harm's way. And even if there are few of them left, they can significantly help with their stunning ability.
The fact that Luck is taken as a skill will allow you to put some other useful artifact on the Luck slot instead of an artifact for Luck. So the argument about losing a slot is simply absurd. Luck will not be superfluous for any race.