The two are not the same. Just as numerous place names are duplicated in North America, they are also duplicated throughout Europe.
Go to http://www.odessa3.org/collections/refs/link/villhelp.txt
where you will find at least 3 Rosenheim in Russia, one of which is in the Volga River region of German settlements.
For additional help with researching Germans from the Volga River region, check the resources at http://www.ahsgr.org
. Finding a passenger list with their entry to the States (or via Canada) will probably help your search.