Anyone can put an address in their DNS records, whether it's "theirs" or not. I have several records with 192.168.0.0/16 IPs. The DNS can be seen publicly but obviously they don't route. It's the same thing.
Other folks are definitely using those DoD addresses. For example, I see a bunch being announced by AS23352 / Server Central: https://bgp.he.net/AS23352#_prefixes
