You are correct in that Drago (sounds like drahgoh) is a given name, English translation is typically Charles or Carl. It can also be a diminutive of Dragutin, Dragomir, Dragoslav or Dragoljub.It is a very popular name among Croats and Serbs.
Ethnic Serbs of course came from what is now Serbia proper, but also mostly from places in Bosnia and regions of Croatia, such as Lika, Kordun and parts of Slavonia
One may understand why descendents of those farm owners may not wish to discuss this.Perhaps a better way would be to contact the German Embassy or Consulate in your area.
Robert Jerin Croatian Heritage Museum Cleveland Ohio