Traits are not the same as DNA ratios of base pairs of the 46 chromosomes.
As I understand it, if you had someone you already thought was a cousin, DNA testing would show the likelyhood that they were related.
But it is not going to pull those relations out of a larger database. The combinations and possibilities are too immense.
DNA Identification Technology
http://dna-view.com/DNAtechID.htm#kinship
I think I said, since they have letters and correspondence, they could use DNA to screen candidates. I agree, if they had to start cold DNA by itself wouldn’t be much good.