I interpret "Dream Eaters" as those who keep others away from the darkness, in some form or another. This is why Riku is considered to be Sora's Dream Eater; it technically was his keyblade that prevented Sora from drowning in darkness in the beginning of KH1.This is the first I've heard of King Mickey and Kairi being Dream Eaters...how did that theory come about?
Likewise, every time that Riku comes close to giving into the darkness, Mickey's always there to save him. I think their friendship could be the reason why the KK has a Mickey keychain on it.