These are just theories of some historians that have never been demonstrated. Actually, these "rumors" and criticism against Pius XII come from the fact Vatican remained neutral for most part of WWII, even if the pope spoke many times against racism - many think Vatican could do much more to stop Nazis, others think Vatican preferred to work in secret, remaining neutral on the outside.
By the way, all major forces involved in the war knew about nazi labor camps at the time Vatican reportedly found out what was happening; that's why, especially in recent years, same criticism previously targeted to the Vatican is now targeted also to the major players in the war.
Here is another great and unbiased article on the subject -
https://www.jewishvirtuallibrary.org/...st/Marrus.html - from the Jewish online library.