There aren't really any rules to this.
 
Vanilla ice cream, a fruitier olive oil and fleur de sel is the classic combination, but experimentation might yield fantastic results.
 
Chocolate ice cream with a peppery Tuscan oil and some earthier sel gris would be tasty, for instance.
 
Strawberry ice cream with a Meyer lemon oil and Murray River flake salt would be not only delicious but beautiful.
 
The possibilities are endless.