With respect to the Army aviation helicopter unit, and the other VIP transport helicopters in the National Capital Region, the reason stated for not using ADS-B is that these missions include continuity of government functions, which is significantly more critical than day-to-day transport of very high-level officials (as important as that transport may be).
Law enforcement and med-evac helicopter flights also are involved in the DCA airspace problem. Further, besides the Army unit, reference was made - if I understood correctly - to a unit of USAF. Perhaps this was a reference to the helicopter unit assigned specifically to the White House and was left unclear on purpose.