People are silly if they think "secular law" has no religion in it. Of course, there is religious law in it. It may not be theistic religion, but it is religion. All the horrors of Communism, Nazism, Dictatorships, and such are based on secularism, a religion unto itself.
Nazism was certainly not secular, although there were some high ranking individual Nazis who were highly anti-Christian and Hitler repeatedly expressed anti-Catholic sentiment. Under Nazism, the state and various Christian denominations (mostly Protestant and Roman Catholic) actively coordinated with each other - at least initially, the relationship progressively fractured at the end of the 1930s and into the 1940s.
The NSDAP sought to mobilise Christian fears about 'atheistic Communism' as part of its efforts to win public support. There was also an effort under Nazism to unite all the German churches into a single body, known as the 'Confessing Church', although this was only marginally successful and resulted in lots of pushback from other denominations.
The NSDAP also pushed is own version of Christianity, known as 'Positive Christianity'. This was an ethno-theistic construct based around concepts of Aryan racial purity, loyalty to the Party and antisemitism., playing down the role of Jesus and playing up Hitler as a mythic figure (weird).
There was also an offshoot/alternative Christian theology that developed in the 1920s and 1930, known as 'German Christianity' and was supported by the Nazis. This mixed in elements of Lutheran and Evangelical theology with various older German traditions dating back to the days of the Holy Roman Empire.
Dictatorships aren't necessarily secular either. There are a number of existing dictatorships that are official Christian at present, and plenty of examples from the 19ths and 20th centuries (Franco, Habyarimana, Salazar). Not to mention all the other religious dictatorships.