Not Shetlands, which have been bred for fine, single coated fleece.
If you mean 'Vikings' in Britain, then probably the multi-coloured, multi-horned 'land sheep' or tan face would be the thing. They were found throughout Britain I believe and are thought to be the ancestors of our modern 'primitive' breeds such as Hebs, Shetlands, Manx Loughtan, North Ronaldsays and so on, each of which has evolved to suit their particular environment and the needs of their shepherds.
However, it is thought that the Romans were the ones responsible for introducing finer fleeced sheep, which gradually became the amazingly fleeced animals that England's wealth was built on. So highly bred white sheep were around in Viking times, however that is defined, but perhaps only in monasteries, and the old type were more prevalent amongst the general populace.
Soays are often used as being primitive sheep, but perhaps more in the pre-Roman time.
There are of course various breeds which claim to have been 'brought over' by 'the Vikings' - not the invaders but the farming settlers. The hard evidence for that is missing but it is often claimed for example that multi-horned sheep are Viking in origin. However, the archaeological evidence shows that multi-horned sheep were around in the Bronze Age, long before the Viking era. It is likely that, as with Hebs, the Viking claim was a deliberate attempt to romanticise the origins of our rare primitive breeds, to help make them more popular.
If you mean Vikings in the Scandinavian countries, then they now have various northern shorttailed sheep, including Gotlands and Icelandic, so perhaps they had a very similar type to Britain.
So, which would be the best breed to use in re-enactment villages? Probably a mix of Hebs, Manx, Ronnies etc, interbred, to give something like the original horned and multihorned, multi-coloured type.