No, only a spouse identified at the time of loan closing who meets the criteria in Mortgagee Letter (ML) 2014-07 is an eligible Non-Borrowing Spouse for a Deferral Period upon the death of the last surviving borrower.
Lenders must obtain a certification from “unmarried” borrowers stating that they are not married and that they understand that the HECM does not contain a deferral of due and payable status for a future spouse. Certification requirements are detailed in MLs 2019-15, 2015-15, 2015-02, and 2014-07.
For additional information see:
Mortgagee Letters at: https://www.hud.gov/program_offices/administration/hudclips/letters/mortgagee
Federal Register 24 CFR §206.34 at: https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=1&SID=c431228bd419ebcafbfda37ecb92005b&ty=HTML&h=L&mc=true&r=PART&n=pt24.2.206#sp24.2.206.b