Life tap, charges, can merc tap life?

[adeyke]

1) Can lifetap be cast (via Dracul's Grasp) on strike by a ranged weapon? (throwing knifes, axes, javs, bows etc?).

Yes.

2) Can the spell (on the gloves) be triggered by an elemental damage strike?

It's not clear exactly what you mean by an "elemental damage strike." As a rule of thumb, "attacks" trigger it while "spells" don't.

3) Once cast (via charges or a necromancer or Dracul's gloves), does it return life for elemental damage?

No.