Many military golf courses have to be creative to "stay in business". All Morale, Welfare, Recreation golf courses on military bases are non-appropriated facilities, which means they do not receive any of your tax dollars to operate. They receive funds from MWR, but are really self sufficient.
Fort Jackson has two 18 hole courses and they offer a limited number of "memberships" to veterans. The catch? YOu have to get a MWR Visa card that they charge your dues to, and they hope you maintain a balance so they make more of a profit. If I lived within 30 minutes of Fort Jackson I would join in a heartbeat.
That said, not all are open to the public, but many are. In fact, if you called an asked the pro, they would mostl likely allow you to be their guest for a round for a guest fee.