Yeah, but calling a (presumably) cute puppy Pluto is either ironic or invokes the original Roman latin cognate of the Greek word "Ploutos" (wealth), and was considered by the Romans as the giver of gold, silver, and other subterranean substances (and only later conflated with the Greek god of the spiritual underworld (Hades), and then the Christian Satan).
So Neptune would be fine, except the dog would probably need to eat a lot more, to get bigger.
Also, Mickey should really get another dog called Charon, and the two puppies be inseperable ... unless Pluto had a sibling that we haven't been told about yet ... ZOMG! Story! ©!