Yes. As a US citizen, you are a US person, and should fill out W-9 instead of W-8BEN to provide your Social Security Number. You can put a foreign address on the W-9, as per the answer to this question.
Reading through the administrative guidelines concerning the German nationality law (page 43 of this link), I found the following paragraphs concerning the loss of German citizenship when a foreign citizenship is applied for and awarded:
Ein Antrag im Sinne des Absatzes 1 ist jede freie Willensbetätigung,
die unmittelbar auf den Erwerb einer ...