Yes you can go to an emergency room for treatment without having insurance or the ability to pay.
But when you do get out of the hospital you'll be billed for the entire cost of the emergency room visit but no hospital whether public or privately owned can deny you services if you visit the emergency room.
A lot of times people who visit emergency rooms are too sick, injured or may even be unconscious where they wouldn't be able to fill out paperwork before getting treated in the emergency room.
It's illegal for an emergency room to deny patients services just because they have the inability to pay.