Clive I think the fact that the documentary was 5 years old is key here.
In the last 5 years we have had a number of landers and orbiters sent to the red planet and they are not all NASA led/US owned projects.
The science that can be done from earth has greatly improved even for amatuers, so it would be very difficult to keep anything 'covered up'
Astrophysics and cosmology is a worldwide science and the information is freely available for people to study and call bullshit on any cover up claims.
From my studied I would suggest its not impossible to go to mars due to radiation, but with current tech, it would be pretty unlikely - its a one way mission anyway, theres no coming back, butwe just have no data on what that kind of misison would do to the human body, they are trying though, Chris hadfield for example, documenting the tests he had to go through after returning from the ISS.
Having said that, I dont think they are going to find anything of huge value on mars, well except very VERY basic life forms, perhaps brought there on a comet/asteroid that has been able to survive the extreme conditions.