They aren't a significant portion of the DoD R&D infra.
Most FFRDCs and UARCs are staffed by civilians employed concurrently with a regional University or Industry Vendor, and these labs in turn are PPPs often operated by a private sector firm like Lockheed or a university like UCB.
On top of that, the bulk of the budget goes to funding research done outside of FFRDCs and UARCs via programs like DARPA, grants from the DCTO S&T, SBIR/STTR, etc
This fusion of university research, private sector research, and some limited in-house research is what's called Civil-Military Fusion.
The issue is the private sector portion has increasingly been divorced from the private sector, as up and coming private sector opportunities or promising startups don't have an easy on-ramp into the existing defense procurement or research infrastructure, and grantwriting+compliance overheads plus limited grant funding dissuade most companies aside from your Charles River Analytics types from going thru the hurdles.
