Do cards that prevent cards in graveyards from being targeted by spells and abilities stop cards such as Crucible of Worlds?
Your intuition is exactly correct - Crucible of Worlds doesn't target the land cards, so Ground Seal doesn't prevent it from working.

This is reinforced in the Gatherer rulings for Ground Seal:


  Only spells and abilities that target cards in graveyards will be affected. Abilities that don’t target cards in graveyards (like the one Tormod’s Crypt has) can still affect those cards.