Ethan appears 64 times at rank 1608 on male pets. This is a top-10 American baby name that has drifted into pet registries through owners who love the name and see no reason to reserve it for humans — or who named the dog after an actual Ethan they know. Both are common paths.
The Baby Name Spillover
Ethan has been a top-10 American baby name consistently since the early 2000s, driven partly by its biblical roots (meaning "firm" or "enduring" in Hebrew) and partly by its two-syllable ease. The generation that grew up with Ethans as classmates is now naming pets, and familiar human names become pet names through that proximity. The human name is at /names/ethan.
The Mission: Impossible Layer
Ethan Hunt — Tom Cruise's character in the Mission: Impossible franchise — gives the name an action-hero register that suits energetic, capable male dogs. A dog named Ethan Hunt is a dog whose owner has given him the most impossible of mandates. Belgian Malinois and German Shepherds fit the capable-action-hero register well.
The Counter-Reading
Ethan on a pet is warm and completely inoffensive — there's nothing to explain or defend. The name is so familiar that it generates no friction, which some owners find reassuring and others find slightly boring. For an Ethan who earns his name, neither matters.