yes, Kassler would be someone from Kassel, Leipheimer from Leipheim and Luttenberger from Luttenberg, but this surname (i'm talking about Reidinger) has ing in it and that makes it possible that it's not a surname deriving from a placename at all. Reiding and Reidinger are also surnames in the Netherlands. Other variants are: Reitsma, Reids, Reidsma, etc. They all mean 'son of Reid'. Reid is a Frisian name, probably from the Old Frisian word rîda , meaning 'driving, walking', related to the Dutch word for knight: ridder . The surnames Reidinger and its variants are thus Frisian, but doesn;t necessarily mean that they originate in the Netherlands, because the Frisian people live near the coastlin of the whole North-Europe, stretching from the Netherlands to Denmark. That explains why these surnames, especially Reiding and Reidinger, are found in Germany, Denmark and The Netherlands.
About Dornhagen, i can't but agree, but an extra note: dörnhagen as a whole word has the meaning 'thorn-hedges', which in Dutch is doornhagen . So the village with this name was probably a place with much thorn-hedges.