Yeah, I'm with Cloak. The first words of Jake's description were "My first reaction was that someone had cloned a person and a deer together." Which, to me, strongly implies a centaur-oid shape. Also, the next paragraph mentions that Elfangor had to duck his head under the doorway, which those fan-art creatures don't really look capable of doing (on the other hand, that sentence in the book just brings up the question: why don't Andalite ships have doors big enough for Andalites?)
Also, how come none of the fan-arts have tail-blades? I know that's mentioned in the initial description of Andalites (although I think it's referred to as a 'horn' or 'stinger' rather than a blade, but still, some form of tail-weapon is definitely present). And some of the fan-arts' extra eyes don't even seem capable of independent movement, let alone anything like the typical Andalite stalk-eyes? Again, that's canon from the get-go.
I do really like the artist's concept for the hooves, though. And the fact that they all have a very 'herbivore' feel to them.