No. Grim Harvest gives you the ability to reap life energy from the enemies you kill with your spells (PHB 118). The full text is:
At 2nd level, you gain the ability to reap life energy from creatures you kill with your spells. Once per turn when you kill one or more creatures with a spell of 1st level or higher, you regain hit points equal to twice the spells level, or three times its level if the spell belongs to the School of Necromancy. You don't gain this benefits for killing constructs or undead.
The triggering component is the direct effect of your spell killing the enemy. It also must be a spell of 1st level or higher to gain the life.
The magical effect of Teleporting the rock to a height above the enemy is just that. Everything past there is the mundane effect of a falling rock and gravity. Similarly, teleporting the target X feet above the ground doesn't kill the target; instead, it is the resultant fall from a great height, and the associated damage from the fall, that kills them.
Expanding beyond the initial focus of the spell Teleport, Grim Harvest will trigger in response to a spell the player casts that kills one or more opponents, but not constructs or undead. The base requirement is that the text for the spell states damage will be dealt by the spell or it kills the target out right (Power Word Kill). Lacking any mechanics stated by the spell, or in the case where the lethal blow is determined by another rule, such as falling debris, falling damage, drowning, or even dismemberment through Flesh into Stone, Grim Harvest won't trigger.