I've gotten into this argument before, and I don't really feel like rehashing it in its entirety But here are my main points
1. Kandras are infiltrators. They are trained to be perfect spies. Standing out in any way, even as little as Felt does, would not be in character for a kandra.
2. There's no reason for a kandra to retain Scadrian bones or Shin eyes. The epicanthic fold is just a fold of skin. A kandra could fix that in seconds, even without taking new bones. But given the decades of war, there's plenty of spare bones around. A spy would want to blend in perfectly, not retain conspicuous bones.
3. A scout is generally sent off on, well, scouting missions. Not near where decisions and events take place. That's not a good position for a spy. A servant or scribe or something would make more sense.
There are more that I don't remember off the top of my head, but I really don't think Felt can be the kandra. Mrall is my suspicion of choice.