I have a 1996 Atlanta Olympic bottle of Korbel champagne. Are there collectors?
Yes. There are pretty much collectors of every type for almost any item imaginable... anything that is old, or even remotely interesting, is likely collected somewhere in the world by someone.
A simple search for "bottle collectors" turns up many, many results, including one for The Federation of Historical Bottle Collectors. Who host a "National Antique Bottle Convention" yearly.
Another search for "champagne collectors" similarly returns many, many results, including various social media groups like this one on Facebook called "Champagne Collectors."
By definition, your item is collectible - it's suitable for being collected (as according to the merriam webster dictionary,) and it is less than 100 years old, as stipulated by this article from Antique HQ. Whether or not this particular bottle is considered particularly collectible is subjectively based on the collector(s) themselves. Basically, if someone wants to collect it, then it is a collectible. If you yourself have collected it, then it is a collectible.
However, appraising an item like this is a matter in and of itself... if there is a market for this type of item, this task is easier. When the item is more rare, it's basically left up to who will pay what for it... meaning, if someone wants to buy your bottle for $1 or $1000, then that's what it's worth.
To support this fact, I will reference the old "banana taped to the wall" incident - in which an artist simply taped an old banana to a wall during his exposition. An art collector bought said banana for $120,000... and promptly ate it.