The Third Reich defined Jewishness as racially-inherited, not religious and used a family's genealogy to prove whether one was Aryan, Jewish, or Mischlinge (mixed-race). Joining the NSDAP or other governmental agencies required one to prove their racial pedigree. All public employees were required to have an Ariernachweis (Aryan certificate) that proved that there were no recent Jewish converts, or any Jewish ancestors in their family. For membership within the NSDAP, applicants had to prove their Aryan pedigree to 1800, for SS members, to 1750. The expansion of state power and agencies like the army and RAD which were compulsory organizations made it harder for converts to pass. One of the curious byproducts of these laws was that the keepers of Jewish archives became relatively privileged, or at least semi-protected, Jews within the Third Reich though 1940/41 as they often had the paperwork that proved an individual's Jewish genealogy came before the arbitrary cut-off dates set by the regime.

So, no, conversion was not a shield for German Jews. It added confusion for areas of occupied Europe like France or the Low Countries, but where there were a number of Jewish converts, but the Third Reich was able to import the methods they had pioneered within Germany to define Jewishness as an ethnic trait defined via genealogy.