Album title is english translated as Rite of the Black Sun. It's pretty much a straight reference to SS and Wewelsburg. And then album has symbolism and lyrics leaned towards right (even if not the most NS out there).
Why is this tagged as NSBM? I don't read Finnish, but I put the lyrics through Google Translate. It seemed like the two English songs had the closest resemblance. There were some nationalistic lyrics and even a little glorification of "our race", but I didn't find any racist, separatist or hateful themes. It wouldn't come as a huge surprise if the men behind Nattfog were in fact right-wing extremists, but I can't see any obvious Nazi beliefs (or racist/fascist/separatist/prejudiced beliefs for that matter) in Mustan Auringon Riitti's lyrics.