While all Kingdom Hearts Originals are Disney characters by legality and IP ownership, the general understanding is that anything Original ( Sora/Kairi/Roxas ) has a ton of creative freedom from Square and Nomura's end. They need to be family-friendly in design though.
I think we can broadly guess and characterise it in these ways:
A ton of creative freedom:
- KH Originals
A lot of creative freedom:
- Maleficent, Pete, Goofy, Donald, Mickey, Yensid, etc.
Varying degrees of creative freedom:
- Most Disney films
Low creative freedom:
- Frozen