Well, sure, technically he is right - a judge should look on the inside....
It's just that what someone willing wears on the outside might give you a pretty good glimpse of what is on the inside. Now, on a "freedom of belief" scale, sure he has a right to believe his Nazi crap. He even has the right to dress up as one publicly. But his children need a good up-bringing. His children deserve a good life, all children do. Having your father give you names associated with Nazism is not a sign that he understands what is needed to give your child a good life. At best, his naming policy demonstrates gross, gross, gross stupidity. At worst, he demonstrates that he is selfish and doesn't care what effect the names will have on his children. So either he's an idiot or he's nasty. In either case, he doesn't deserve custody of his kids.
Also, he's illiterate, or only semi-literate. How can he provide for his kids?
The only issues is - are the kids mother any better? She slept with someone who wears a Nazi uniform in public, so her judgement isn't exactly the best either. We might be looking at a case in which neither parent is fit to raise these kids.