Many Jews went into hidding or escaped, I belive.
The best way to find the truth would be to find individuals or their relatives who can tell you in detail, just what transpired and how they were treated by specific people.
Also, the Hungarians were known to kill the Jews, and they were in Serbia, killing both Serbs and Jews. Then you had the ethnic German residents of Serbia - Volksdeutch (sp) - who joined with the invading Germans. If they were residents of Serbia or born in Serbia, they could technically be called "Serbians". Therefore you have to be careful when there is blame for Serbians that they are ethnic Serbs. To be assured of that, you'd have to get their names.
I believe that most died. According to one book, 6% of Serbia's Jews survived. The number may vary, depending on the source of information though.