No, slots have nothing to do with it, they are just stored relative transforms that get decomposed and passed in to the plugin. You just need to make sure that the relative transform being used for the slot calculation is relative to the bone, and not to the mesh itself, that may be an oversite in the BP side of the template ( need to check) as I never specifically tested slots on per bone gripping. Should be easy enough to override and I could modify it in 4.25+ to handle it correctly.
You passing out a neck bone name as the slot just makes it use the location of that bone as the slot.
Slots have no logical effect on the gripping in the plugin (outside of a true/false in the melee script), they are a construct on the users end. The optional snap socket is a helper utility that I actually tend to suggest that people not use in favor of manually passing it in, as its more fully controlled on the users end when they pass it in.
Edit
Yeah it just needed a couple of node changes:
https://i.imgur.com/2wtND8U.png - Using the correct world transform with slots
https://i.imgur.com/1tKtaPZ.png - Changing it to pass out the bone name with slots as well.
those changes are live in a new template commit.