To answer my own question, I found this from googling https://support.gog.com/hc/en-us/articles/4408596960797-Disco-Elysium-The-Final-Cut-M1-compatible-version?product=gog
Which seems to indicate that it is, but you have to take some active steps to make sure that's what's run when you actually play the game. I find that a bit confusing but it sounds simple enough. I don't know what GOG galaxy is but I assume it's a storefront like Steam. Sounds like if you run by opening Galaxy and hitting play, it won't be the native version and will run through Rosetta 2 but if you run it from your applications folder it's the native version. This is a bit odd because that makes it sound like by default what you have installed is BOTH versions which sounds like an awful waste of disk space but maybe I've misunderstood.
After I bought the game I went looking for where to download it and found it in the games section of profile page on GOG but when I downloaded it, it was an installer that starts downloading the Galaxy thing. I can't imagine having any use for that and since I'll likely never launch what will at the moment be my only GOG game from there it's just a potential source of confusion so I clicked on the download backup installer option. Hope this ens up being native, I think the game is meant to have very modest requirements indeed in any case so if it turns out to somehow be running through Rosetta 2 I suspect it'll be imperceptible anyway.