There is signs that (some) Vikings had something we could describe as dreadlocks (as many other cultural groups). Roman documents have for instance descriptions of some Vikings wearing “rope-like” long, strands.
The reasons why some Vikings had rope-like strands, could have been practical reasons (instead of religious or stylistic reasons, that can maybe be a reason from for instance from India or Greece). Vikings were of course not the only group wearing rope-like strands, also Celtic and German tribes did (and maybe also for the same reason).
We don’t know for sure of course but dreadlocks in Historical ages could have existed for religious reasons in for instance Sadhus in India or ancient Egypt and for stylistic reasons in Greece, New Guineans or Masaai. Other reasons could have been practical. Rope-like strands or dreadlocks can be “easier” when you are “out on journeys”, maybe even in war and battles. It doesn’t require that much daily maintenance and can easily be “packed in” during rain or sunny, dusty days.
Similar to rope-like strands is Elf-locks (fairy-locks) that both Vikings and Celtics had (two groups that also lived close to each other). In Celtic folklore elves appeared at night, to tie knots in people’s hair (which also was unlucky to undo) and it could probably looked like modern braids (for instance Rasta).
Another group is the (Polish or Jewish) Plait, which could be for many reasons but one due to simply not combing. (And tools for grooming hair has existed long before Viking Age, so it is not due to not having tools that would be the reason for rope-like strands).
Clearly we can see that their is not one cultural group that can claim dreadlocks and likewise to belong to them.