Initially, gambling was expected to be seen as a means to why people can come together and have fun, so if in the military camp you discover any form of being entertained there, then it should not be a surprise, because they also need to ease their own self from the struggles in this profession and get entertained in various ways, since most of them may not be able to have access in going to the casino mingling with the civilians, if they gamble together within their territory, i don't think its something bad, after all, gambling is entertaining.
I understand that soldiers also require some means of relaxation and fun but slot machines are an easy way to get into addiction, particularly in a stressful place like being in the military. It is vital to be entertained, however, there ought to be safer ways of entertainment, which would not jeopardize their mental status, as well as finances.