Hi,
there is always the difficulty regarding comparing qualifications from different countries. I would presume if you would have done a PhD in Germany that that would normally also be recognosed as a PhD in the US. A doctorate as such is not by definition the same, yet I would suspect that you would be able to to postdoc work in the US with that. Saying that perhaps it would be a good idea to contact US universities regarding the issue before you start anything to save yourself problems later on!