When you enchant a Tendon Whip, the enchantments only affect an entity when hitting it normally as you would a sword. If you use the long range targeting attack, the enchantments do not apply. This is a bit odd, since when the Tendon Whip extends to hit a target it has a full enchantment glint. It was disappointing when the range attack dealt a measly 5 damage to undead creatures even after enchanting it with Smite IV.