Naruto Wikia says that the Ninken literally is Japanese for "Ninja Dogs". While Viz does indeed does translations on the series that can be fairly faithful to the literal meaning (Fūinjutsu: Genryū Kyū Fūjin literally means "Sealing Technique: Illusionary Dragon Nine Consuming Seals" but the show calls it "Sealing Jutsu: Nine Phantom Dragons". I personally think it is more convenient for recording that they give it the shorter name), the Ninken falls under a technicality.
First of all, Look at this Google Books link to a 1999 book on linguistics:
So, in terms of staying true to the original meaning, would you prefer "hound" or "dog"? For my love of staying true to the original meaning of certain words, I prefer "hound". However, if you are one of those people who likes translations done literally, "dog" is appropriate.