358/2 Days Something the Cheshire Cat said to Roxas... (MAJOR DDD SPOILERS)

It's probably just one of many implicatins throughout the series that Roxas has a heart.
Even before the big reveal in DDD, msot people assumed Roxas had a heart, the game even has scenes like the one in Days where Axel asks Roxas if he's sure he doesn't have a heart, and such.
So yeah, just more foreshadowing, I'd say
If you think this actually means something with the Cheshire Cat, then you are apparently under the delusion that anything that happens in a Disney World that doesn't involve a major antagonist is important

 

Many would probably say that's just Cheshire cat being the Cheshire cat but Nomura is very sneaky and plans ahead so it's quite possible that this was a vague foreshadowing to him having a heart.

 

Even before DDD, some characters believed that Roxas had a heart Axel asks "You are sure you don't have a heart", then there is all that thing that you HAVE to have 2 hearts to use 2 keyblades (something Roxas do even before Sora). I think by the time BBS was out it was pretty obvious that Roxas had Ventus' heart, even before the game was out it was stated that "Ventus had a conection with Roxas" so yeah... the suprising thing in DDD wasn't that Roxas had a heart, it was that the rest of the organization had one as well... the only one that seems to have one is Roxas and maybe Axel , but one could argue that Axel was trapped by the force of Roxas' Heart just like Sora's Heart made the people in Castle Oblivion remember him even though they never met him.

 

I think it was more to reinforce how Roxas felt like an outsider everywhere. The Cheshire Cat's advice, if delightfully mad, would be sound for anyone else - but the rules were different for Roxas. He was different. And it may have turned out that the Nobodies did have hearts, but it was the feeling of lacking, of longing to be someone else, to belong somewhere, that drove many of them.

 

In the first Kingdom Hearts game, he says that he has all the answers, but doesn't always tell. So i think it's likely that he did know Roxas had a heart.
Plus in DDD

Spoiler

you find out nobodies do have hearts

So yeah, he may have been aware of that.