“Federal law requires certification of a candidates qualifications”
There is no such law.
That is simply a form the DNC used to notify the 50 states who their nominees are so that the 50 states can put the persons on the their ballots.
Federal law does not regulate the National Conventions or how the parties choose to conduct their business.
You might just be right there. I can find no FEC forms requiring certification, only registration and even then nothing really but a name on the form.