Hans Viebig is listed in the book by Veit Scherzer
Ritterkreuzträger 1939-1945. It states that he was born on May 31, 1897 in Berlin, and died on September 30, 1961, in Rheydt. He was also a recipient of the DKiG on September 11, 1944. He received the Ritterkreuz on February 21, 1944, and had the rank of Oberst as Kdr. of GR 258. Which agrees with the two websites, but does not
prove that he is the WW1 ace. But it is certainly very suggestive.
Enjoy!
Frank.