Yo is certainly one of the most unusual words I come across as an Austrian in Germany. In fact, I am not even sure how it is spelled, because the Duden has nothing to say about either Yo or Jo, and I did not find it in any other dictionaries either. The spelling Yo chosen here is motivated by the fact that the English word Yo (extensively used by Jesse in Breaking Bad) is pronounced exactly as Yo in German, see here. Whether or not the German Yo comes from English I do not know yet. More information about the English Yo can be found here.
While little information about Yo is available in books or online, it is very commonly used by German (but not Austrian or Swiss) native speakers. In English, Yo is used by certain (young) people as a greeting, see here and here. In contrast, in German, Yo seems to be used to either express agreement (instead of Ja, Jawohl) or simply as a filler between or at the beginning of sentences (similar to Na gut, Gut, Okay).
Perhaps this post can inspire a discussion that sheds some more light on the origin, spelling and use of this word in Germany.