This has been a topic which has given me some considerable amusement in the rec.arts.sf.tv.babylon5.moderated newsgroup, and I thought I'd share with you my take on the subject (considering I can't post to the rotten thing!).
Are cats Vorlons? Well, they may do amazing mid-air catches of their prey for their own reasons, have their own agendas and when they do deign you with a comment, it's barely intelligible (well, unless it has anything to do with food) - but Vorlons? Come on! Ever tried sticking a cat into a catbox (read: encounter suit) and keeping it in there longer than five minutes without it breaking loose, biting/scratching your face off, swiping irritably at anything it can reach of you - even if it IS for its own good? Impossible!
So does that leave Shadows, then? Well, I'm not wholly convinced on that score either. Sure, they are self centred, create chaos when they're of a mind to just to see who will survive it and completely dominate their "owners", making them do everything for them (even to following them around to ensure it is done!); but really, cats couldn't give a monkey's **** which way the universe turned out, whether it's the strong or the weak that come to dominance. As long as people do as they instruct, they are happy.
Anyway, below is a list of the arguments for and against that have come through so far, then following, the Great Maker's (JMS himself!) thoughts on the matter...
These have been altered slightly
to make sense in this kind of listing!
* Nobody fully knows the extent of their powers (How *do* they know when we're about to open a can of tuna?).
* They care about what happens to us (or we think they do...), but they have their own agenda.
* They constantly battle the Shadows (read: dogs). The battle goes on year after year, but neither side ever wins.
* They manipulate others to get what they want.
* They're always saying things, but it takes a special type to understand them.
* They have been known to fly through the air.
* They'll attack anything that looks like a spider.
* They have always been here (or seem like it).
* After a battle, they go to sleep.
"...They are neither... Cats are Keepers... they sit on your
shoulder, they're invisible unless they want to be seen, they glare at
you out of one baleful eye, and gradually they take over your life."
JMS on 29th January 1998