If you'll allow me to rephrase the question...
'Is a spirit of kitten-eating-evil (as opposed to a spirit of intellect, or a spirit of air, as Bob is alternatingly described), evil by nature (as Bob would be intelligent by nature)?'
Do I have it more-or-less right?
Yes, that basically sums it up. I guess it's really a question of how much free will something has when it is, by it's nature, evil, as viewed by humanity/mortal culture
in general. I don't think there is much point to debating absolute evil or good, I'm more interested in a "from the PC" viewpoint.
To go with something less esoteric than a SoKE, how about the Malks? Described by Bob as "to cats what Hannibal Lecter is to people" (assuming more "cruel psychotic killer" than "eater of own kind"), and shown in Heorot to take great joy in terrifying pretty much everything and causing painful death. So I think we can call them evil.
Now, can you have a nice one? A malk sick of the "torture people like cats torture mice" game and out to instead protect little children and stray cats? To set ground rules, I'm not talking about a malk that has been altered by its interaction with a mortal of powerful will (Jim B. has mentioned that Toot-toot is changing due to his service to Harry, so that's an outside agency altering the spirit's nature). I'm talking about a malk who maybe started out to find some nice human children to torture and eat (or just torture), and got sick of the game and started protecting them.
Possible? Why? Why not?