I don't interpret what Rivers said as in any way offensive to Jews. I interpret it as a reminder, by a play on words, of what the Nazis did to the Jews. She doesn't want people to forget the Holocaust. There's nothing unusual about that. We are always being told that each generation must learn about the Holocaust, lest we forget, and quite right too.
What Rivers said is only a 'joke' insofar as it is a play on words, the words 'hot' and 'German' in particular. If anything it pushes home the point that many of the Jews who were killed by the Nazis were Germans. Some of them will have been more 'German' than Hitler.
It is not an offensive joke. It is a reminder of something offensive. Something we need to remember.
I thought Klum looked reasonable from the waist down and from the neck up, but the supposedly 'hot' bit was simply in bad taste. But that is just a matter of taste, I suppose.