Hamburg was pretty much leveled doing WW2, so you will find many new buildings like in DC, and many reconstructed buildings, but the style is distingtive Northern German and while I will agree that at a distance the building style around the Capital Building do indeed resemble the buildings style around the inner Alster lake the look and feel up close is very different... the green cobberroofs are a faved used roofing tradtion from Northern Europe that I guess could have been used for inspiration in DC..
In conclution some parts may look the same but the feel and actual look is very different... atleast IMO