I'm not sure what the rule is on that score, actually. Looking at the German barons category there seems to be an even split between those with Freiherr in the title and those without. Considering most of his life was lived in a German republic I would be more inclined to leave his title out but if somebody else wants to include I wouldn't mind. For me though, leave it the way it is, for the sake of convenience as much as anything. I'll look for a reference later on.