No truth at all.

Popes are elected by cardinals; it is not a 'title' that is 'given'. During Hitler's reign the popes were Pius XI (until 1939) and Pius XII (from 1939).

Also while the Vatican is located in Rome, Italy, since 1929 it is not part of Italy. It is an independent state which was neutral during World War II.

Since my flair touches on this subject I felt I should chime in as well. /u/edXcitizen87539319 is 100% correct. The pope as a religious office is elected. Pius XI was elected in 1922 and served until his death in 1939. His successor (Pius XII) was elected in 1939 and served until his death in 1958. The pope as a head of state was the leader of the Vatican since 1929, when the Lateran Concordat was signed. This document made the Vatican an independent nation, surrounded by Italy but not a part of it. At no point was there an alliance between the Vatican and Germany, especially given that Article 24 of the Lateran Accords requires strict neutrality in foreign affairs for the Vatican. There was the Reichskonkordat that was signed between the Vatican and Germany in 1933, but this bilateral treaty contained nothing approaching an alliance.

At no point was Hitler given the title of pope.

If you are interested, I have written about the Vatican during WWII previously on this subreddit.

By the way, Vatican City was a country of its own rights back then. It was not part of Italy, de facto or de jure, since 1929.

Interestingly enough, Mussolini had a role in this.

http://www.britannica.com/EBchecked/topic/331566/Lateran-Treaty