I'm afraid the maypole is an import from England - Moore gives the following quote re Mayday celebrations (see www.manxnotebook.com/fulltext/folklore/ch06.htm):
Fifty years ago the celebration of May-day Eve was still very general, as will be seen from the following account extracted from the Mona's Herald newspaper of the 5th of May, 1837; but now it has almost died out :–" On May Day eve the people of the Isle of Man have, from time immemorial, burned all the whin (gorse) bushes in the Island, conceiving that they thereby burned all the witches and fairies which they believe take refuge there after sunset. The Island presented the scene of a universal conflagration, and to a Stranger, unacquainted with our customs, it must appear very strange to see both old and young persons gathering particular herbs, and planting them at their doors and in their dwellings for the purpose of preventing the entrance of the witches."

no mention of maypoles and in fact Dr Clague - (www.manxnotebook.com/fulltext/mr1911/ch01.htm )states explicitly - these customs are not Manx - though it is possible that the mostly English born garrison at Castle Rushen adopted the English custom of gather in the May - certainly the 19th Century Manx Methodists would have been equally hard on the custom had it existed.