I see this as backwards logic for the look of Thor, Asgard, and Thor's brethren. True they are the gods worshipped by Nordic ancients(including Germanic peoples), but they are not Vikings. Of course as we recognize the methodology of creating gods and myths; Nordics would visualize their gods as appearing like them, but for the purpose of this film the inhabitants of Asgard are real and not the imaginings of the Nordic people. The Asgardians in this film exist independantly and presumably for countless millenia prior to the Viking culture, and so the appearance of a Viking(beards, fur clothing, etc.) should not necessarily influence in exacting detail the appearance of Asgardians. Jack Kirby did not straightjacket Asgardians into Viking apparel.