I don't know that we can discount the terrorist surrogates so quickly. There may well be more terrorists and more anthrax already in place. And it could well be in reserve until it can be employed in a devastating attack -- and it may not necessarily be connected with Saddam's downfall.
As you note, though, Saddam's agents are subject to the same temptations that Rumsfeld is putting out there for the battlefield soldiers. It is conceivable, in fact, that an agent of Saddam, with sufficient cover, might just walk away and make for himself a new life in the land of capitalist plenty.
There is also a possibility that the people chosen for this particular task are among the most devoted and fanatic.
While I believe the CBW threat can be defused at home and abroad by the dialogue Rumsfeld is offering, I still believe it likely that the home front will suffer more casualties via CBW than the battlefield.
More than conceivable, when you consider what financial inducements it would make sense for the U.S. government to offer such a person.