I don't think Lutheranism in KotR is as radical a departure from Roman Catholicism as it is in real life - it's mostly an anti-Byzantine, anti-Papal, pro-German nationalism movement that says the HRE doesn't need to listen to any stinkin' pope.

If it weren't for the Pope issue, I imagine that it would be a secular movement akin to the hyper-nationalist movements that defined the rise of facism in the 1920s and 30s.