Hey @Ranson, no problem at all!
Both the Blackheart Blade and Hammer are similar to two other weapons dropped by the Champion of the Warmaker, except that they have lower stats. It might not be as obvious by their description, but they also imitate the fact that “unworthy wielders may not be able to wield them as weapons” ( as per the description ), meaning that thralls should be unable to use them properly, which is intended.
In short, the Blackheart weapons and the Warmaker’s are not intended to be wielded by thralls, so dealing no damage is the intended behaviour.