Re-opening of the casinos is a risky move for me because just a single host person that is inside the casino can infect all of the people that are inside of it. Also, take note that there are some hosts that are asymptomatic ones so you don't know if he has the virus or not.
If they care about their lives then they shouldn't risk it going to a casino and it would be better if they will just gamble online rather than going there and talk to other people which can be affected by the virus.
With fewer people in the casino due to the limit of people who can enter a casino, if security will be strict is not that difficult to implement social distancing. However, what you said is correct there are hosts that are asymptomatic so securing the safety of people who will enter the casino is not secured with all the precautionary steps they will take.
I guess the government and casino operators have no choice since the gambling industry brings a lot of income to the government and the number of employment they can provide. So, I guess it's a risk they have to take to keep the government and businesses running.