Dorman is now extremely rare in Germany at the moment: only 20 names on the german Telephone directories. If you look at the list of Dorman immigrants in USA you will find many more british Dorman than german Dorman. And no Dutch Dorman. Instead you can find quite a few russian Dorman. In Germany DORMANN is more common than Dorman and in Amsterdam I have found DORMANS. The german surname Dormann or Dormanns come probably from the word "TOR" in english "gate", it is a locative surname because it indicates a person living by a "gate".