A number of games have been termed “Viking chess” by other writers, though I generally avoid the term altogether because it is both ambiguous and inaccurate. Both hnefatafl and kubb have been called “Viking chess”, as well as at least one actual chess variant.
The problem with calling hnefatafl “Viking chess” is that while hnefatafl and chess are both board games, their invention and development were totally independent of each other, their physical form bears very little similarity, and the fundamental strategies of two games are based on two very different ways of thinking.
The problem with calling any actual chess variant “Viking chess” is that it is inherently anachronistic. Chess was introduced to Scandinavia by the returning crusaders after the Norwegian Crusade. The Norwegian Crusade, at the dawn of the 12th century, came on the heels of the end of the Viking Age in the 11th century. Viking Age scandinavians played hnefatafl, but by the time chess was introduced they had abandoned Viking Age culture, adopted Christianity and begun embracing medieval continental European culture. Some surviving chess pieces likely made in Norway in the first half of the 12th century more closely resemble their Persian predecessors than their late-12th century Norwegian successors, representing a mid-12th century assimilation of chess into Scandinavian culture, but even those early 12th century chess sets were created during the Medieval period, not the Viking Age. Since chess was unknown in Scandinavia until the Medieval period, there was no version of the game that could accurately be called “Viking chess”.
The problem with referring to kubb as “Viking chess” is, firstly, that it is not even a board game but a lawn game. Secondly, kubb has two small and simple armies of kubbs and a single, shared king, in contrast to chess, which has relatively large, complex armies and two independent kings. Thirdly, the development of kubb cannot be reliably tied to either chess or the Viking Age. If kubb was in fact invented in the 20th century as an attempt to reconstruct an earlier but poorly understood game, then it is neither “Viking” nor “chess”.