I believe, like in most serious war/action based movies, humor is only used between the soldiers when they are joking around. This is normally never in the middle of a firefight, but there is always that one cocky guy who says some smartass remark just before his death.
Being a soldier also means you are apart of a brotherhood, and every soldier gets along at one time or another. Weather it be since basic training, or just before their unavoidable deaths. You will always see (in a good movie, anyhow) a certian amount of acceptance between soldiers. Even if they do not agree with eachother, brotherhood finds them in the end. I hope we get to see this "bonding" in the fan film. Not every soldier is as emotionless and serious as Bruce Willis' portrail of Lieutenant A.K. Waters in "Tears of the Sun". Heck, even Rambo had his emotional conflict in the newest "Rambo" movie. I hope we get to see this too in the film.
As long as the combat is realistic, the soldiers movements are as close as possible to soldiers of today (or in the future-I'm sure their movements/tactics will not have changed much), and the combat is believeable (PLEASE no "one squad takes out 30 brutes without any casualties, and without the use of larger, more deadly weapons" crap) I will be happy.