Slip Sliding Away, as the say!
History has taught us to routinely recommend a rough broom finish on the concrete floors of car wash facilities simply because of the high risk of slipping and causing serious injury.
Keep in mind that the floors aren't merely wet with water, but often have high lubricity detergents and surfactants... along with various spray-on protection products that all leave a slippery residue on the floor.
I would think that an epoxy floor, even with anti-skid additives, would risk becoming a virtual ice skating rink, given an accidental chemical spill. Even some concrete sealers have proven too risky for car wash staff.
Imagine a serious hydraulic leak, and the havoc it might create.
Plus, we must remember that many employees don't wear safe foot-ware, often relying on flimsy sneakers that slip more easily when wet. And those sneakers collect residues from various chemical areas of the wash... or tire dressing from the finishing area. Once you mix the reside-coated sneaker footing with the normal chores at a car wash, and then expose those workers to a coated floor; watch out!
Between the insurance companies and the ever-present army of slip-and-fall lawyers looking for income, you'll rue the day you did anything that made things even a little bit more risky at the car wash.
Enough said?
Steve