Patents have to be issued to individuals. As a federal employee any patents assigned to him as a consequence of his work as an anthrax researcher actually belong to the government per an agreement executed at the time he was hired.
Everybody knows that.
But Ivins didn't mail the anthrax.
Ivins did indeed own the anthrax vaccine patents. And yes, Federal contractors can patent their discoveries. It just depends on the nature of your employment contract. They wouldn’t get any researchers to work for them otherwise.
Just a matter of terminology. The inventor(s) has/have the right to the patent, but may assign it to the government, a company, or any person. An assignment works to transfer rights from one owner (in the case of a patent, the first owner is ALWAYS the inventor) to another.
When patents issue, they will be in the name of the inventor, and may include a naming of an assignee.