While I do agree that the lines that describe the act should be slightly changed, I don't think the damage should necessarily be raised.

Hell, with the way the damage is, it's merely slap on the wrist. For the most part you could get rid of the "A zombie of the dangerous horseman's burning hands scratches him." line and it would still be accurate, less spam, and descriptive.

I think the few hp penalty that is incurred from vulnerabilities such as your example is "good enough" to make a point, but not dangerous enough to actually do any lasting damage. To put it another way... If the zombie were to hold onto the silver hammer for a few seconds, it would get hurt significantly... but it is immediately dropping the item, much akin to a person putting their hand by/into flame. If you were to stick your hand into the flame, you'd get pretty burned. If you go close enough your reflexes, or in CF-terms your fire_vuln, causes you to pull away maybe getting slightly burned to teach a mental lesson.

I don't think the damage needs to be upped at all, though perhaps the wording cleaned up. Cosmetic changes are pretty low priority however.