Nope. That's incorrect. It didn't matter if you had converted to Catholicism, according to the Legal Mischling (Mixed Blood) Test A , If you had two grandparents who were Jewish, you were considered to be a "Mischling First Class." A “Mischling Second Degree” is a person with one Jewish grandparent and three non-Jewish grandparents.
Further, from Esther Littman Gorney who was a Holocaust survivor:
According to the Nuremberg Laws of 1935, Jews were divided in four categories:
1. “Volljude” or full Jew: a person who had either four or three Jewish grandparents
2. “Geltungsjude” or self-declared or believing Jew: a person who had two Jewish grandparents and two non-Jewish grandparents (Aryan) and was raised in the Jewish religion
3. “Mischling First Degree”: a person with two Jewish grandparents and two non-Jewish grandparents, who was either baptized and brought up Christian or practiced no religion
4. “Mischling Second Degree”: A person with one Jewish grandparent and three non-Jewish grandparents, who was baptized and raised Christian or with no religion
According to Littman Gorney:
"The Nuremberg Laws dictated that Jews could only marry within their own category. A Mischling, for example, could not marry either a full Jew or a Christian. I was a Mischling First Degree because I was the offspring of parents who were also labeled Mischling First Degree. That means both parents had Jewish fathers and non-Jewish mothers. Both my mother and father had been baptized as Lutherans."
Link to full article:
Toland said this was specifically the rule so that Jesus and Hitler both qualified as Aryan.
Hitler worried that he might be a quarter Jewish by blood, so this law cleared him.
And since Jesus's father was God (not Jewish) and Jesus was a Christian, therefore Jesus was not Jewish. (All of which is silly, but the Nazis created this rule in an attempt to convince Christian Germans that Nazis were not anti-Jesus.)
Well, that's what I remember Toland writing.