Not only are Halewijn and Halloween essentially homophones, but this story bears a strong similarity to the Scots-English ballad "Tam Lin," of which the holiday Halloween bears a central presence. Do both of these words and stories have a shared source?
While the song Halewijn has several analogues in the English ballad tradition, I don't believe any mention a specific holiday.
Not only are Halewijn and Halloween essentially homophones
I would not say that at all. /ˈɦaːləʋɛi̯n/ versus /ˌhæləˈwiːn/.
Halloween is from "All Hallows' Eve",the eve of All Hallows' Day, AKA All Saint's Day. (In Dutch that'd be Allerheiligenavond)
Halewijn derives from the West Germanic name Hailwin (whole-friend). Essentially all Dutch names that end with -wijn (e.g. Boudewijn, Alewijn) and English ones that end with -win (e.g. Baldwin, Edwin, Alvin ) are from that same suffix.