I don't like the idea of Nobles as Heroes, since the Barbarian, Thief, Giant, are all very un-noble IMO, going by their nature. In my view, I don't think Samurai should have been there from the beginning, but since it is, Viking wouldn't be too out of place.
If I were to indicate a personal viewpoint of DK1's restriction on the Heroes, maybe DK1 seems to have been based on variants of medieval Europe setting, it seems to be consistent in DK1 Hero depictions and is only broken by the Samurai. In that setting, even if there were no Viking, there might still be something looking similar to the Viking in the line-up, perhaps under a familiar name of Barbarian or even simply Berzerker.
For the Monster-pick in DK1, it seems to be built around a few staples and a few originals, so I don't think it comes from all lands / religions / folklore. There are a lot of creatures / ghosts in many other folklore all around the world, most of which are not present in DK1.