If the main entrance is level (i.e. doesn't have a step) then the ground floor will almost certainly be ADA compliant. Some elements will be grandfathered in, such as old front doors, but everything inside that had to be built when that restaurant/bar moved in (bar, bathroom, partitions) will need to be compliant, including bathrooms and turn radii. If the restaurant is over 30 years old then there's a good chance that most things will probably be grandfathered in and non-compliant.

(not an architect, just work with a bunch of them)

I second Pet Shop. I also like Porta, Mathew's, Wurstbar