Definitely an interesting question about lounge access. When going through the Lufthansa City airlines website about lounges it simply has a link to the Lufthansa.com lounges webpage. So are all *G granted lounge access? Are there carve outs for UA/NH/AC *G like EN and EuroWings?

Edit: I found the footnote about lounge access as written on Lufthansa.com:

"Entry with a boarding pass for a Star Alliance flight. Passengers with a boarding pass for a flight with Air Dolomiti, Lufthansa City Airlines, Eurowings, or Discover Airlines will have access if they are Star Alliance Gold members of United Airlines or Air Canada. In addition, passengers with a boarding pass for a flight with Air Dolomiti or Eurowings will have access if they are Star Alliance Gold members of All Nippon Airways."

-RM