Dolphins will always lead to the nearest Ocean Ruin or Shipwreck unless distance < a certain amount(regardless of whether or not it contains no chests with loot) in which case it will search for the further of the two.

Dolphins ignore the Y coord of of a general structure location, so they'll typically end up hovering over a structure location (this works almost identical to /locate).

Dolphins also seem to ignore buried treasure structures in every scenario I've tested.