I personally don't think it's a good idea. (Just referring to the cat here).
As cool as it may sound, there is SO much that can go wrong. You'd likely need to hire someone to make sure the cat stays put, the cat could get nervous, try to bolt, see something that's more interesting to him than your wedding and try to wander off, etc. etc.
I could see if it was a dog. Dogs (depending on the individual) live to please their people and will do just about everything for them. Cats... well - WE are THEIR slaves. As far as they're concerned, you are there to pet them at their will and fill their bowl and adhere to their will - not the other way around.
I foster for a cat rescue, along with owning my own cat. My cat is the most chill, mellow, 'whatever-to-the-world' cat I have EVER seen. There is no way ANY cat (of the 80ish we've fostered) or my cat would be willing to put up with that.