Correctamundo!
Not once, not thrice, but in between.
Our loyal companions can be seen. -----You can see dogs twice in the game: Treno and Conde Petie.
With friends by side, and running behind ----In Treno the moogle is always running behind the dog, and in Conde Petie the it trots along with the owner.
They really are not hard to find. ---- Considering how you have to go to each of these places, you're guaranteed to see both.
"Shakespeare only names us once!" they say, ---- Merchant of Venice. Crab is the dog. It's the only dog ever named by Shakespeare in his plays. (the Bible mentions a cat only once, you can see where I got confused)
But tell me, friends, what are they? ---Um....yeah...obvious.