According to Lucy, there's a procratemod on these hammers. This is one of the fields not shown in the standard item view, but listed in the detail. The higher it is, the more often the weapon procs, at a given dex.
Hammer of Judgement - proc rate: 250
Hammer of Divinity - proc rate: 325
Hammer of Souls - proc rate: 450
Hammer of Damnation - proc rate: 530
What that means is, all these weapons proc like crazy, but the higher ones are progressively MORE likely to proc. How much more likely isn't obvious to me.