I do have a brother named "Udo", and as far as I know, it is a masculine given name (Wikipedia), but to be fair, the only other Udo I do know of was the late Udo Jürgens. Then there's Udo Shigetaka (https://tigertranslations.org/2020/01/15/flower-field-demon-king-0/ or https://www.novelupdates.com/series/ohanabatake-no-maousama/). If it is following the rules for Japanese names, Udo is a surname, and Shigetaka is the given name. Is that right? Do you know of another word that is a given name in one country and a surname (family name) in another?
Udo/Uto is a Japanese surname, yes. It's written as 宇戸. It roughly means 'house door'. Ai-chan personally has never met someone with the surname Udo, though.
They know, they are of German ascendence, Udo a name that is not that rare. That is not the point, here...