Yep, the Nazis are far from the only ideological ... or really just any kind of group to use skull / skull and cross bones type imagery, more broadly, its... well just a commonly recognized symbol of death and mortality, and can and has been applied in various contexts.

But, yeah, as you say... in this context... its pretty fucking clear the branch of ... symbological (sp?) meaning they are intentionally descending from.

And... well the unfortunate modern truth of it is that many symbols have been essentially taken, or claimed or colonized, whatever, by Nazis. The swastika itself is an example of this, I'm not a super duper expert, but basically, the original meaning of the symbol was... in the context of Hinduism/Buddhism primarily around India, and it symbolized something like luck, life, renewal.

But the Nazis famously took it, mirrored it, and ruined it, and also confused the fuck out of a lot of Westerners who only understand the symbol and Aryans via Nazism, when... both topics/concepts have much deeper and interesting histories than simply being something the Nazis appropriated.

Heck maybe I'm remebering my own American history with rose tinted glasses, but I could swear that in the 90s, the Gadsden flag had not been so strongly linked to the... 'so libertarian/ancap they actually overtly flip and become loudly racist fascists' crowd... granted, I was a kid in the 90s, but my impression was that the actual Nazis hadn't quite cottoned on to using the Gadsen flag, back then they were just mostly using out right Swastikas or KKK derived symbology.

Metallica had a damned album that was basically a subdued, recolored Gadsden flag, the black album, in '91, and while they're obviously not saints or philosophers, I wouldn't go so far as to call them just actual fascists, at that point in time.

But all that with a grain of salt, thats just me trying to remember my white trash, white supremacist adjacent, evangelical upbringing.

Update: Here, yeah, Hetfield seems to be somewhat dismayed about how the particular song, and gadsden snake imagery, was warped into having a meaning that he says he did not mean to convey:

https://www.ultimate-guitar.com/articles/features/the_story_of_the_artwork_on_metallicas_black_album_and_the_unexpected_band_that_inspired_it-161365

Metallica's use of the image was a reference to the second single from the album, titled "Don't Tread On Me." As for his use of the image, he said this in an interview with MusicRadar in 2022,

"'Don't Tread on Me', I love the song, but it shocked a lot of people, because everyone thought it was pro-war when they thought we were anti-war, and alls we're doing is writing songs, we're not standing politically on any side. 'Don't Tread on Me' was just one of those 'don't *** with us' songs, and obviously referencing the flag and the snake and what it meant, that all tied into the black album and the snake icon on the album cover, and I think it's great to play that song live. We're over here in Europe playing it, and people aren't appalled by the songs. We haven't played it in Iraq or Iran yet, though."

Yeah I mean... "we're basically dumbass fence sitters and we just want to make cool music with extremely broad market appeal" isn't exactly commendable, but holy shit are there ... way, way more overtly fascist metal bands, at least nowadays.