Did any of the norse/celtic/nordic cultures ever have dreadlocks as a major hairstyle? I remember finding information on the topic several years ago for a school project, but now when i search for it all i find is really irrelevant information.
The TL;DR is we have no actual way of knowing, but probably not, considering the (relatively rare) evidence that we do have.
Taking a look at the bog bodies, their hair was combed, washed, and cut before interment. Tollund Man, Grauballe Man, Lindow Man, and Cashel Man all have hair that is fairly close-cut.
In the sagas, we have scenes of people washing their hair, and Haraldr háfagri was remarkable for not cutting or washing his hair until he gained his kingdom.
Additionally, manuscript images from the time show hair that is either close-cropped or shoulder-length, but never in dreadlocks.