Not sure what you are asking as Feds pay SS not States. However, they do look at state law:
This section describes the procedure for determining that a non-marital legal relationship (such as a civil union, domestic partnership, or reciprocal beneficiary relationship):
can be treated as a marital relationship for purposes of determining entitlement to benefits; and
meets the duration of marital relationship requirement.
The Social Security Act allows us to consider the claimant to be the number holder (NH)’s spouse for benefit purposes if the state of the NH’s domicile would allow the claimant to inherit a spouse’s share of the NH’s personal property if the NH died without leaving a will. Under these circumstances, we will treat the couple’s relationship as a marital relationship.
