Is it possible for a EU national (with planning) to be married in Germany?
Surely - why wouldn't it be?
On a slightly related topic, a friend living in Vienna married a German girl. To satisfy the German requirements, he had to get a "certificate of non-marriage", to show he was not already married. Of course such a thing does not exist in the UK, but the Embassy in Vienna obliged by scribbling some suitable words on the back of an envelope, or whatever, and accompanied it with an official stamp, for the sum of 120 EUR. However, it transpired that this would not do, and he had to go back and get another certificate that said that not only was he not married to a woman, nor was he married to a man.