I've had the same problem with kills not counting, for Stormcaller, St. Ydwen's Redeemer, and the Greenstone Staff. Going through Raedric's Hold, human kills seem to count for the generic enemies counter, but other monsters and creatures do not. St. Ydwen's Redeemer also is not registering normal OR proc kills on vessels - it is stuck at 6, even though I've let my wielder fight through plenty of guls and revenants alone and kept track to make sure that she's been getting normal weapon kills.