The concordat was signed in 1933 BEFORE any foreign power was in battle mode to oppose the Nazis for atrocities. Prime Minister Chamberlain signed his deal with the Nazis well after this and American bankers were still backing Hitler financially after this as well. On 14 March, 1937 Pope Pius XI published
Mit Brennender Sorge which stated the moral incompatibility of and conflict between Nazi racist ideology and Christianity. It's clear from the text the Pope is aware that the Nazis have violated and broken the concordat and that the Holy See opposes their ideology. Funny the bigots always fail to mention this. [?]
A copy of this is available online at Mit Brennender Sorge : http://www.newadvent.org/docs/pi11mb.htm