I see that only Humans, Nobodies and Heartless are allowed as Races. May I have the exception of making a vampire/elf/other humanoid character? They do fall under the category.
No. Vampires, elves and other such humanoid races were never on the KH series as playable characters. Yes, they are seen in Halloween Town, but they were never playable. Your character must be a playable Race, nothing else. Please follow the profile sheet as is.

Can I play a canon?
No. Canons are NPCs. We decided upon this because people went overboard at one point by godmodding and even had an arrogant attitude just because of who they played.
However, you are allowed to play them to get your RP going as long as they stay in their world. For example, you may play Captain Jack Sparrow, but he cannot leave Port Royal.