No, it most certainly is not. The number is based on the Lancet 2 study which found about 650,000 excess deaths. Tim Lambert at Deltoid extrapolated the Lancet 2 excess mortality rates to about one million because Lancet 2 ended just as violence in Iraq was increasing enough to make further field work impossible. See
http://scienceblogs.com/deltoid/2008/11/deaths_in_iraq_1.php for more information.
In general, Iraq Body Count is an obscene underestimate of excess deaths. IBC data comes from two sources (1) english language journalist accounts and (2) Iraqi government data. We know that (1) is absurd because when violence increases, deaths increase and reporters' presence on the ground decreases dramatically. If you read journalists' accounts of their own work in Iraq (for example, Imperial Life in the Emerald City by Rajiv Chandrasekaran), you'll note that in many cases reporters simply never left the green zone. How could they possibly write stories about killings when they can't leave the green zone? We know that the data from (2) is highly suspect because much of the conflict in Iraq has been sectarian with government death squads engaged in ethnic cleansing. For example, we have evidence showing that when Shiite religious parties took control of the ministry of health after elections, they fired Sunni medical staff and imposed policies restricting the treatment of wounded Shia. If the Shia run ministry of health won't treat Sunni victims, why on Earth should we trust them to faithfully record statistics about how many Sunnis were executed by government death squads? I mean, are we normally so credulous that we accept death counts made by the government accused of making the killings?
From a scientific perspective, IBC's "analysis" is garbage and should be ignored. At the very least, you have no business citing IBC unless you understand enough about IBC's methodological flaws to explain precisely why it can only be considered a gross underestimate.