It's not even a discount. Sometimes it's just moral support.
Every NASA space center that involves dangerous activities has a select few restaurants and bars that everyone knows by name. The same goes for Navy and Air Force bases that involve dangerous activities. For example, there is no Building Zero on the JSC campus (building numbers start at one, which is the main administrative building). Nonetheless, if you tell people "we're getting together at Building Zero after work", nobody needs directions.
Before this bar, astronauts and engineers hung out at the now closed Outpost Tavern, formerly known as The Ultimate Joint. It's the astronaut bar in Apollo 13. Edwards AFB had its Happy Bottom Riding Club (watch The Right Stuff). The only centers that don't are the ones that don't do dangerous stuff.
It's a bit difficult to give a bar a "Certificate of Appreciation". A restaurant? That's not a problem. I've been to multiple NASA centers and multiple Air Force and Navy bases. Each one has restaurants that have pictures on the wall. Here's one in the JSC area:
There are multiple restaurants in the neighborhood of NASA JSC, NASA KSC, NASA ARC, JPL, Edwards AFB, Fort George Meade, and China Lake that have certificates exactly like this; I've been to many of them. I've never been to the Delamar Dry Lake area.
For a place such as that (aka "the middle of nowhere"), it's not that hard to get such a certificate. All you have to do is serve food that is better than cafeteria food. Note well: From the online reviews of the Windmill Ridge, the food there is downright good, much better than cafeteria food.