The dealership is private property, so I can't possibly speak for exactly what charging rules they allow.I see those on plug share. Never tried it. You're saying that say Nissan (one near me) doesn't mind me coming in with my Tesla and charging on their dime? Nice of them. Just a little surprised.
That said pretty much every dealer-based CCS charger I have clicked on in Plugshare.. has comments from random people about how happy they were to charge to their Bolt, Mach-E, ID.4 etc on that particular charger. My guess is the dealer had the CCS charger installed to charge the EV they sell & service and those vehicles get priority. As long as the dealership vehicles aren't using the charger.. then probably care less that someone else plugged in. A few bucks of electricity is easily worth the foot traffic that could possibly sell a new $60K vehicle.