That recipe has been tested with the corn starch so it's fine to use.

Agree with Sheila. There is no need to omit it when it is in a tested and approved recipe. Any separation that might happen with a relish wouldn't be apparent anyway as it would if used in pie fillings and the other recipes where some try to add it.

The primary reason for the restriction on cornstarch is because it is a thickener not because it separates. When an approved recipe calls for a thickener there is no problem. But it does not mean it can be used in other recipes.

Dave