Hummers vs. HUMVEEs

The primary US military vehicle is the High Mobility Multipurpose Wheeled Vehicle (HMMWV or Hum-Vee).  A Hummer is a civilian version of the same vehicle with many bells and whistles and horrible gas milage.  They are not the same.

Fraternization

Despite what is sometimes implied in Stargate: SG1 officers can date officers, and enlisted can date enlisted.  The reason Major Carter and Colonel O'Neill can not date is because she is under his command.