While there isn't a conditional ignore on the Individual Relationships like there is on the Constituent mapping, you can use the Area Settings in conjunction with Field Settings on the First Name field to suppress Individual Relationships that you do not want to add. (To learn the difference between the Area Settings and the Field Settings, please see this knowledgebase article.)

For example, if we have a file that contains a relationship between a student and a parent, but we only want to add them if the Parent Relationship field in our file indicates Mother, Father, etc., then we can use the Field Settings on the First Name field to only add the First Name when the Parent Relationship is not blank (see screenshot below).

Using the Condition above will result in the First Name field being left blank for any record that does not have a Parent 1 Relationship value populated regardless of whether or not they have a Parent 1 First Name value.

Next, we should set our Individual Relationship Area Settings to not add a relationship for any record missing a First Name (see below).