While not a direct answer to your question since much of the response covers other areas & times & doesn't specifically mention Norse Viking raiders, and certainly more can be said on the matter, u/Rhodis did touch on militarized clergy in the borderlands between Christian & pagan kingdoms in early Medieval Europe in an answer to [a question I asked] (https://www.reddit.com/r/AskHistorians/comments/6pzd49/how_common_were_fighting_churchmen_in_medieval/?utm_source=reddit-android).