Yes, they are the same option. The "Enforce relationship for INSERTs and UPDATEs" option in the DDT is the "Enforce Foreign Key Constraint" option in SQL Server Management Studio. It basically says whether the constraint is on or off.
ALTER TABLE tablename NOCHECK CONSTRAINT foreignKey;
We disabled the combo boxes because we decided that it didn't make sense for the constraint to be off but still cascade the deletes and updates, but it looks like SQL server allows this scenario.