Right so like you realize that the source for the imagie, the "edelweiss.abovethetreeline.com" source, is not a fansite or anything, its a site for cataloging what books are being published by who run by publishers themselves apparently.
So unless some crazy TLK fan went in to this site to sabotage it so their OC would look canon or something then the source for that image IS DISNEY
The image is of crappy quality congratulations, but it still from a source that is run by Disney or at least Disney-Hyperion, which is their publishing arm. The cover is probably just a crappy placeholder thrown together by people who aren't the actual graphic artists to serve as a placeholder until they get the actual art in. Consider the image of Bunga from the second image you linked, if you zoom in there is still white border around him because that's the standard clip art Bunga, not anything actually put together for that cover. This one just happens to be more obviously crappy that the others, and when it gets updated with actual graphics drawn for the cover it will probably look like the first or third image you linked, since those look like they were actually drawn for the book cover.
As for who the cub is, again they're probably just some crappy clipart that someone had lying around and threw on the cover until they get the actual art. I don't know who claimed it was their character or whatever.
So it is legit in that it is indeed from Disney, but is not legit in that it was probably thrown together by some intern rather than by the actual people who do the graphics work. That or some TLK fan went in to sabotage the site, but again that site is not a fanart site, its a book publishing site, so I doubt anyone would just be able to edit it however they pleased.