I've never heard any evidence of this in particular happening to Prisoners of War in Vietnam, though there was plenty of mistreatment, torture and extrajudicial killings, it should be pointed out that this occurred depressingly regularly on all sides, we probably have the French's 'judicious' use of the guillotine to thank for those lines being drawn early. I guess in this case it was used as a metaphor for what war will do to the young lives thrust into it and even for all those around them. Some may unexpectedly benefit, some my lose everything, but most will suffer in some form or other. Apparently the roulette coda it was lifted almost wholesale from another script the film-makers had possession of that had nothing to do with Vietnam. Top film with some amazing performances, though its still somewhat controversial to this day (can't be that controversial thinking about it as a pastiche of those scenes went on to sell some sort of chocolate selection thing). Platoon captures the experience (yeah I was there, you don't know unless you were there maaaaan) of that war better, Apocalypse Now the insanity, Full Metal Jacket the futility, but none capture the impact on the lives it touched quite like that. Casting director deserves a knighthood, all of them so young, all of them would either become their generation's greats or wonderful character actors (apart from poor John Cazale, a sad loss of wonderful talent).