I think he's omitting some unflattering stuff about his time being drunk in Croatia. Does it make him a Nazi? Not really. But the way he tells the story, like it was a groupthink bonding thing, sort of makes it sound like someone else made the decision for him.
He's either lying about that (it was his choice) which is bad or he's downplaying the kind of shitheads he would hang out with while in the Marines, which is also bad. Seth Harp wrote a book about how some of these unsavory characters can operate within the military.
https://www.rollingstone.com/culture/culture-features/fort-bragg-cartel-murders-1235394302/
Now I won't go so far as to say he joined a gang-like organization while in the Marines, but it can't really be ruled out. And yes, it can't be ruled out that the organization was Nazi-adjacent or Nazi-sympathetic (like a prison gang would be).
I can see how he would be ashamed of it, but like he said, if he believed it the tattoo itself stood for something that needed to be concealed, wouldn't he also have tried harder to cover it up?
So, I don't really know what to make of it. More information could come out, and I will drop my support if it turns out he was lying or if it turns out he supports or condones white supremacy in any way.