Tbh, I like the idea of the whole Zodiac theme- obviously it is very pick/choose heavy because GameFreak definitly didn't plan on it from the start. But, it does get further and further away from being a thing. The only thing shared among all fire starters to date is that they all end up on 2 legs.
But, here's the real question; let's say just for shits the final evolution for fire-croc is without a doubt serpentine, similar to Serperior; being that Serperior has 2 really smol arms. Would the final evolution having 2 really smol legs count for it being a snake? Like I'm talking as small as Serperiors arms. Because if the answer is no- then we would have to say that both Serperior and final-evo-fire-croc are not snakes because a defining characteristic of snakes is that they have no limbs.
On the other side; lets just say for the sake of the zodiac reach-theory that Fuecoco's final evolution breaks the established theme of bipedal fire-starters; and is without a doubt a snake, would that confirm the Zodiac theme?
I'm neutral on this and couldn't care less; personally I'd say it does confirm that's what the theme they are going for now- and taking liberties. However; if it is just a fire-croc, legs, arms and all, that would definitvly disprove the Zodiac theory. And thus, the only thing fire starters share is that they all end on 2 legs.