Organisations with the Individual Relationship destination have additional options that allow them to customise what they would like to happen when non-constituent spouses are matched to their constituent spouses in the Importacular Review screen.
While reviewing a specific record, you can click on the Match Setting icon (shown in the middle of the screen below).
Once opened, the Match settings give the options below.
The default option ignores relationship settings, but you also have the option to create a new constituent and link the two via an Individual Relationship or to import the data in the data source, but ignore certain fields (such as first name, nickname, etc.).