You are completely off base here -- it is extremely useful and important to know that the DNA in JonBenet's underwear belonged to a "white male" who is not a member of the Ramsey family.
You are mixing facts together here innapropriately.
They knew the DNA in her underwear was not from a member of the family as soon as they analyzed it. They had all of the families DNA to compare it to from the start.
The analysis might have been delayed due to technical limitations but it was not DNAP technology that exonerated the Ramseys.