It looks like more than a graphic change may be needed. The only lifetap spell I could find in classic with that graphic was the Spectre Lifetap. That's a a 30% increase in hp drained, i'd like to find more evidence. You wouldn't have been able to test this since the spell assigned to the pet may be wrong.
It is mentioned in the comment below:
http://everquest.allakhazam.com/db/s...04540789045975