I think there's a good chance that it was inspired by a Jewish tale, the story of Rabbi Honi. The story goes like this:
The Rabbi was very proficient in Torah and very well known in his town and all around by all Jews. However,he was not especially fond of a social life, and found the company of men to be tiring and frivolous, although he did have a family. He often found himself taking isolated walks along the town paths and enjoying nature while contemplating the Torah or life.
On one of these walks, the rabbi finds an old man planting a certain tree (I believe it was a carab tree). The rabbi scoffs at the old man, "You old fool! Don't you know that this tree takes 70 years to grow! You'll never live to see it grow, and this is completely futile and worthless!"
The old man smiles, and answers, "Oh, I'm very much aware of how long this tree will take to grow. When I was young I took a seed from a tree that my grandfather had planted when he was an old man, and now I am planting a tree for my grandchildren to enjoy its fruit."
The rabbi scoffed at the answer, and decided to lay down on the grass due to feeling particularly depressed. He had no sooner closed his eyes when he fell into a deep slumber. Night came, and he had still not woken. Morning came, and he had still not woken. Night came again, and he had still had not woken. A group of stones appeared around him so as to shield him from passerby, and the rabbi slept on and on and on, until finally 70 years later the stones disappeared and the rabbi woke up from his slumber.
Looking around, the Rabbi saw that it was darker than when he had left his house, and was worried that his family would be concerned over his seemingly hour long disappearance. He started back toward the way home, but was stunned when he beheld a great tree not too far from where he had been sleeping. He walked up to the tree and found a young child eating a fruit. He asked the child, "Did you plant this tree?"
"How could I have planted this tree?" responded the child, laughing. "It takes seven decades for this kind of tree ago. My grandfather planted this when he was an old man and now I'm eating its fruit."
The Rabbi was shocked beyond words. He had an inkling that not all was the same as when he went to sleep. He started walking home, but soon realized that the streets he was walking were nowhere near like the ones he had walked - from his perspective - only hours before. Eventually, after a while of being unable to find his house, he told a passerby that he was Rabbi Honi. The villager looked at him oddly and said, "That's impossible, Rabbi Honi disappeared a long time ago." Slightly deterred, the rabbi asked him where Rabbi Honi's family lived.
He went to the house and hesitantly knocked on the door. A younger child opened it up, and the Rabbi asked him, "Is this where Rabbi Honi's son lives?"
The child responded, "Rabbi Honi's son died many years ago. I am his youngest son."
"Then you must be my grandchild!" the Rabbi exclaimed, and went to hug the child but stopped when the child backed up uncertainly. The other family members came to the door and the Rabbi saw that none of his relatives recognized him for who he was. He had originally shunned society when they were willing to accept him, but now that he needed society more than ever they were not willing to accept him, not even his own family. He called out a prayer to God to take him out of this living Hell and God relented, and took his wearied soul up to heaven.
There are some big similarities between Rip Van Winkle and the story of Rabbi Honi, but one of the biggest reasons I think it did not necessarily come from a German tale is that most likely the German tale came from the around the 13-14 centuries or so, while Rabbi Honi lived in the 1 century.