Carl Eymann wrote in1969 an interesting document about the assumed heritage of the Eymann family. It has been made available by Ralph Eymann in 1999. You can download it at http://www.imanfamily.net/downloads/imans.pdf.
I think it is very well written, but needs to be commented by several historical facts we know today (by comparing many informations through the Internet), which were not available back in 1969.
First of all, the name Eymann is not of noble or aristocratic heritage. The crest has been manufactured at some time between 1850 and 1900, probably upon request of one of the family members.
Second, there are at least two separate Eymann families in Germany, from both of which family members emigrated at one point or the other to the US. The family originally from Alfhausen, Germany (near Osnabrück) is different from the family originally from Oberdiessbach, Switzerland. The Swiss family was of Anabaptist/Mennonite faith, the Alfhausen family not.
Carl Eymann (the author of the pamphlet), is a descendant of the Swiss family. Ewald Eymann (read page 4) was a descendant of the Alfhausen family. Carl did not know this, and thus mixed both families. In the remainder of the pamphlet, and when talking about his own family, Carl references the Swiss family.
Ewald Eymann, who appears prominently on the first pages of the pamphlet, was a seaman, first in WWII in the German navy (as 3rd officer on a small vessel), later as merchant captain travelling to the US, Brazil and Panama. There is no proof that his story about being a German spy, even about speaking Russian language, is true.