Is it common to do a MS in Germany and then a PhD in USA?
Admission to a "really good" PhD program in the US depends much more on what you do than on where you do it. If you do well and can show aptitude for research, you will have a good chance at many excellent universities. 

Admission, however, is very competitive and there will be many people applying to top programs who have nearly perfect academic records. That will be the biggest issue, not the institution at which you study. Make sure that you can get excellent letters of recommendation by the time you wish to move on. 

As for "common", however, I don't really know, but suspect it is about as common as applying from good institutions (like Dresden) from any other country.