Sure no masks and what may appear crowded is not really that, high ceilings, powerful HVAC heat exchange systems which bring air from the outside and overall low population density in the urban areas make Vegas seem actually a pretty safe place compared to say packed motels during Gra or Spring Break.
P.S. on an anecdotal note about 6-7 years ago after BH USA I’ve personally witnessed a person that was all sweaty and coughing like they are about to die being escorted by security of the floor after about 15-20min of being around the tables.
While I don’t have any sources on to confirm this policy, it really wouldn’t surprise me if casino security monitors people who seem to be ill if nothing else than to avoid the optics of having medics on the casino floor.