I think he could definitely be an animagnus, but it wouldn't surprise me if he never did anything with it. Also, a ferrett isn't exactly the most prestigious of animals. I could see his father giving him a bad time about turning into a ferrett instead of a more noble creature. A ferrett would definitely fit Draco. Also, JKR doesn't seem to put events like that in her books unless they are foreshadowing something that will show up in the future.

But it wouldn't surpirse me if he wasn't an animagnus either.