They've probably picked the best few airframes out of the 50ish f117 there were, perhaps used various bits of airframe from various planes. Possibly even applied some new RA materials to the f117 to better represent new threats.
The F-117s in these shots are looking factory fresh. Very impressive for such an old jet that has been “retired” for quite a while now.
Still, is it really more cost effective to do all that and use f117 to play aggressor than simply dedicate a few F-35s for the same role? Stealth can always be dialled back with some add-ons to the airframe, if needed.