Apparently there is reason to think so. If they die in Germany or on the way to a German hospital, they're not counted.

http://www.sftt.us/phpbb2/viewtopic.php?t=4006
http://www.dailykos.com/story/2005/5/18/115832/501

"U.S. Military Personnel who died in German hospitals or en route to German hospitals have not previously been counted. They total about 6,210 as of 1 January, 2005. The ongoing, underreporting of the dead in Iraq, is not accurate. The DoD is deliberately reducing the figures. A review of many foreign news sites show that actual deaths are far higher than the newly reduced ones. Iraqi civilian casualties are never reported but International Red Cross, Red Crescent and UN figures indicate that as of 1 January 2005, the numbers are just under 100,000.

There is excellent reason to believe that the Department of Defense is deliberately not reporting a significant number of the dead in Iraq. We have received copies of manifests from the MATS that show far more bodies shipped into Dover AFP than are reported officially. The educated rumor is that the actual death toll is in excess of 7,000. Given the officially acknowledged number of over 15,000 seriously wounded, this elevated death toll is far more realistic than the current 1,400+ now being officially published. When our research is complete, and watertight, we will publish the results along with the sources In addition to the evident falsification of the death rolls, at least 5,500 American military personnel have deserted, most in Ireland but more have escaped to Canada and other European countries, none of whom are inclined to cooperate with vengeful American authorities. (See TBR News of 18 February for full coverage on the mass desertions) This means that of the 158,000 U.S. military shipped to Iraq, 26,000 either deserted, were killed or seriously wounded."