What actually happens here is that the game ends with your HP -over- 100, thus denying you an EM. iirc, this started happening after zanz fixed a bug with AM healing coming before Poison damage, thus making AM far too effective vs. Poison. The community guessed the order of damage and healing changed, and this started happening. Yes, it's now harder to get EM with vampiric damage. Usually what you do is stabilise your lead before you win so you can either calculate how to get exactly 100 HP or just not take any damage on the previous turn, or you use something like Drain Life to get back to full HP before you attack.
You should change your topic to lifestealing only, because healing works as normal. Use a Heal on the last turn and you'll get EM. Same with Stone Skin or deckout with something like Sanctuary.