I couldn't careless. The 13 Warrior is arguably one of the most historically inaccurate movies ever made but that takes nothing away from the film. It's definitely one of my favorite movies of all time. I've seen it more than 50 times and it's good every single time.
I wouldn't call it accurate, but I wouldn't call it inaccurate, either. In fact, one of the appeals of the book it was based on was it's attempt at realism. It sought to put the Beowulf legend into a realistic context. Is a tribe of neanderthals living into the historical era considered likely? No, but more likely than some demonic beast with no clear origin. The costumes where questionable, but asides from some of the plate armor and the 1500's style Spanish helm, they were "possible," and I'm guessing they just took license to show that these guys were kinda wandering mercenaries.
ANYWAYS, yes, the vikings did not wear horned helms, although some bronze/early iron age priests of the region may have, on occasion. And while I agree that the Nirn =/= Earth argument allows for them to be worn, I hate that argument in general because it usually gets extrapolated to suggest that Nords are MOSTLY unique, which I think is questionable. For example, although they are TECHNICALLY unique from historical vikings, because they wear horned helmets, they are not totally unique from them, because horned helmets are a stereotype of real life vikings, accurate or no.
There's just so many people who think TES lore is 100% original, and fail to see the historical inspirations. For instance, the Redguards homeland of Yokuda was probably inspired (at least in name) by the African Yoruba culture. But most people have never heard of Yoruba, so when they hear "Yokuda" they think "Oh, that's so original, instead of Redguards coming from a place called Aprika or Orabia." I'm not saying the lore isn't unique...just not as unique as some people seem to think. Unique is easy, it's gibberish. But using historical inspirations in a unique way is awesome, because you can "see" the same sources the devs saw when they were writing the lore. And that allows you make guesses about how those races "might" differ from others. If they were all unique, all things would be possible, and the differences between Redguards and Kahjiits would only be fur.