From questions regarding such on Quora:
Vikings encountered black people enough times to give them them the moniker blámađr, literally blue men. The major encounters between the two seem to be interactions with the Moors, and Viking raids on various North African and Arabian cities. There also seems to be some possible minor occurrences of trading and undertaking pilgrimages to Jerusalem. However, there is no historical account of a blue man joining a Viking tribe. There is, however, a story of a chieftain's wife giving birth to dark-skinned twins, which upset the chieftain and resulted in the twins being given up and later taken back in after three years had passed.
Edit: Looking further, it seems there were a number of reports of dark-skinned Vikings from that era.