If indeed it is German, it's probably related to:
Redmann
North German: topographic name for someone who lived in a marshy place, from a term meaning ‘boggy terrain’ + man ‘man’.
German: from a Germanic personal name composed of the elements rad ‘advice’, ‘counsel’ + man ‘man’.
Found at:
http://www.ancestry.com/learn/facts/fact.aspx?&fid=10&fn=&ln=Redmann