Things that Points to Walrus being Rool
They have basically the exact same bodyshape. Yes, his face looks kinda flat to have a croc-snout, but this is a game, and just like cartoons, remove a mask and stuff that doesn't fit pops out.
The Penguin sees the Kong Hut and immediately informs Walrus, and Walrus laughs and attacks. Of course, most villains would laugh, but to me, it felt like he was happy to get some revenge on the Kongs or something.
King K. Rool often dresses up, and this could simply be a evolution of his costumes.
His Final Battle would appear to take Place on the top, on his boat, which is also the Final Battle with Rool in the first DKC, right?
They both wear a cape (I Think? Or did I make that up?)
And that Retro probably knows how the lack of Rool and the Kremlings effected the fans. Since there are so few islands (though, with more levels in each), it wouldn't surprise me if, when you beat the Walrus, he is revealed to be Rool, and flees to a nearby Island covered with Kremlings.
I may look into this too much, but personally, I actually am suspecting that may be the case. Thus, Rool may have a shot at Smash.
EDIT: Oh, and Another thing. There are a LOT of Walruses as enemies in this game, and the Big Bad guy is clearly a Walrus. I Think they would have the bad guy a exclusive animal, and not just a slightly worse of a common enemy. ^^ Yes, King K. Rool is clearly a bigger, fatter croc, but that was then. :3