Camping by "non-military affiliated" folks?

Are there ANY circumstances whatsoever that would allow someone with NO "military" or "U.S. gov't. Civil service" affiliation what so ever to camp at an RV facility on an ACTIVE military base? Here's why I ask: my wife's sister & her husband were recently told that they WOULD be permitted to camp as a "guest" of someone who's retired military & they'd like to camp on an ACTIVE military base with US (I'm retired from active duty), but I just can't see HOW they would qualify to do so as neither had served any time in the U.S. military nor have they ever been employed by the U.S. Civil Service. HELP?

Sure - many military campgrounds do allow "sponsored guests", which is what they are asking you to do. You, being qualified, would be their "sponsor" (and responsible for their actions). But not all facilities allow guests. Much of it depends on the location, time of the year, and how busy they are. The only way to know for sure if guests are allowed is by calling the facility directly to learn of their current policy on guests.