There's not much point testing DNA in those cases because it doesn't help you decide if consent was gained.
(I agree with your post, btw.)
* which is fraught with its own ethical pitfalls re. DNA storage, but is in line with current US legal mores, if not your or my personal ideals on privacy.
For example, while VAWA talks about non-gendered domestic violence, in practice only one partner is arrested so the other can be allowed to take care of children and in 100% of cases where both parties got into a physical altercation it is MEN who end up in jail and with a restraining order.
But even more interestingly the study showed that men and women choose different method in physical violence, and that has a major impact on injures. Men favors unarmed methods by the use of their hands, while women favor knives or improvised weapons. In average the unarmed method cause more often damage which need the attention of medical help, while armed combat during domestic violence causes more damage in those rare instances where medical help was needed. The explanation for this is that combat with improvised weapons is simply harder to do than unarmed.
Except grabbing DNA information from private companies databases is only potentially useful IF those kits are tested. Testing the kits is orthogonal to clearing the cases.
While I strongly object to mass DNA testing of the type proposed here, the DA's comment should be read in the light of the huge backlog that exists for testing rape kits. Denver, CO's clearance rate is only about 30%, and there was until recently a strong bias towards testing cases involving stranger assault but not assault from family members: http://www.endthebacklog.org/denver
So without endorsing the DA's call, it us based on a legitimate public policy issue rather than purely emotional grandstanding.