Based on the combat that just occurred, I wanted to see if anybody else could verify. I don't know if this is a bug or working as intended, though.

When the "Destroy's Vessel's" enchantment goes off and it kills a vessel, has anybody else noticed whether it does or does not count on the "kills a vessel" counter?

It doesn't count. I had Eder go into the skeleton room with the weapon equipped. He only got credit for 3 kills; the same number as times he didn't get destroy vessel.

Does not count at the moment. I think it's a bug.