In the state of Michigan are the sellers required to disclose an easement?

It depends.  The seller's disclosure statement, if it applies, asks about easements.  Also, title companies require sellers to sign an affidavit disclosing any unrecorded easements.  And if a buyer asks about an easement, a seller has to disclose what the seller knows.  But bear in mind that recorded easements are disclosed in the title insurance commitment that the buyer receives.  Too often buyers don't look at the commitment or request a copy of the documents disclosed in it.  If this easement was laid out in the commitment, it was disclosed to the buyer, even if the buyer did not bother to read it.