[@MegaOscarPwn] You're biased, and I don't see any objective data here.  Besides, given that the Japanese designed a sword specifically to handle Mongol raiders, I suspect they could have figured out something to handle Vikings as well.  The two groups never really encountered each other, so you don't know what innovations would have come of it.  I suspect the issue with knights was more that knights were not used to hit and run tactics, and their idea of a battle was two lines charging at each other, and only knights taking down other knights.

When it comes down to the martial arts themselves, it becomes more about the techniques as opposed to how they're applied.  So the question is really if two copies of the same person had one trained as a viking and the other trained in "weeb martial arts", which one would win.

And given that this is ww2 era with guns and land mines and trench warfare and even guerrilla tactics, where your melee skills are not necessarily so important, suddenly it doesn't matter so much which martial art you studied nor what heritage you have.  Know enough to stay alive long enough to kill the other guy.  =P