Running NAT behind a routable IP address range AND using a totally different range for all servers, VPNs, and various sysadmin crap? I don't believe it.
There's no way they would be so diligent to use that IP range internally without even a tiny bit of evidence externally.
This is the government, so it's practically guaranteed that there's at least two layers of firewalls between any internal networks and the internet. If any of those layers was installed by an average IT consultancy then they'll have used NAT (because that's what you always do, right?) and hidden 51./8 completely.
There's no way they would be so diligent to use that IP range internally without even a tiny bit of evidence externally.