Your husband can show his SPG Gold card or app at check-in & ask them to extend the courtesy of lounge access. If they do; great. If they don't, be gracious & accept it & don't argue w/ them.

They're not required via T&Cs to offer lounge access since the reservation is in your name & account #, and that would also be true if the reservation was in your name & your hubby was a Marriott Gold vs. SPG Gold.

Cheers.