Before the Black Death I believe many Jews occupied the regions of southern Germany and Austria. These areas today are more conservative and I assume were generally the more conservative at the time, and thus must have influenced their tolerance of them in some way.
At the time there presence was met by ambivalence, but a presence they had indeed. Through Charlemagne's canonical law they were employed diplomatically and financially were usurers(which I realize was considered sinful, however these services were still utilized, and they were thus able to roam freely among the country).
They also tend to assimilate into whatever region they go. Sure there were heavily jewish communities but I imagine many were dispersed throughout urban areas?
It seems, according to wikipedia they still held a large presence in the 1700s and onward. Influencing such areas as the arts. Some of the offshoots of their enlightenment also gave way to extreme assimilation. Why would nationalists oppose this?
It was passed on by the first German nationalist organization formed by pronouncedly conservative veterans who fought against Napoleon and didn't hold much of his enlightened ideals.
To them the German nation was defined by a love for Baby Jesus, Christmas presents and the Ancient Regime.