Maybe other non-essential businesses are opened too?
Well, I don't consider most games in typical physical casinos as part of essentials. Their enclosed nature makes it even more risky. I would just have the good/safe ones outside or in well ventilated areas rather than opening up for business in enclosed space.
They could be essential in terms of contribution to the economy and it's Las Vegas, we know what's the main business in that area, it's the casinos so that could not be essential as we speak.
But geographically and logical speaking, they could be essential for the people who resides there who are mostly relying to gambling and casinos.