I have tried to find out what exactly is or was that penthouse-looking top on the Hotel Monteleone. Someone once told me that it was Duke Ellington's club, but I can't find any evidence of that, or that he ever even played in New Orleans. I asked one of the bellmen at the Monteleone, and he said he had no idea.
You are correct that the name "Duke" appeared on the marquee of the Hotel Monteleone on Royal Street, but it wasn't Duke Ellington. It was the Dukes of Dixieland. The original Dukes were formed in 1948 by trumpeter Frank Assunto, his brother Fred and father Jacinto, or "Papa Jac." The band performed all over the world in the 1950s and 1960s.
After the Assunto brothers died, the band was reborn in 1974 with a different group of musicians, including trumpeter Connie Jones as leader. In April 1974, producer/manager John Shoup and the Dukes leased what had been Louis Prima's nightclub on the top floor of the Monteleone and renamed it "Duke's Place." They performed there for 12 years before leaving the hotel in 1986. The Dukes now perform regularly aboard the steamboat Natchez, when they're not on tour.
The rooftop penthouse you refer to at the Hotel Monteleone is not the club, but a private residence for the Monteleone family, which still owns the hotel. In fact, the Monteleone is the oldest hotel in America still owned by its original family.
As for Duke Ellington, he may not have had a permanent club in New Orleans, but he and his orchestra performed here several times. He played the Municipal Auditorium in 1935 and 1938, then returned in 1951, 1968 and 1970. That year, he performed five nights at Al Hirt's club on Bourbon Street and, more notably, at the first New Orleans Jazz and Heritage Festival. To mark the occasion, Ellington was commissioned to write a new work, The New Orleans Suite, which won a Grammy Award in 1971.
EDITOR'S NOTE: After this story ran, a member of the Assunto family wrote to stress that the "different group of musicians" to which Blake Pontchartrain refers has no connection to the original Assuntos.