It is now clear from testing
Code:
$npc->Damage($h_ent, $h_dmg, 13, 1, true, -1, false);
always does the damage $h_dmg to the npc running the script, giving the message that $npc has taken $h_dmg from your spell Complete Heal. I put the 13 just to test it.
So, this does not solve my problem of having the mob cause $h_dmg to each entity on its hatelist. This function cannot create that effect and my search continues...