Just as a note, night vision isn't going to be much help in caves unless there is a light source of some sort, such is the IR lights that you can get for that purpose. The problem is that night vision doesn't actually allow you to see in the dark. What you may perceive while outside as dark is actually quite illuninated by moon and star light. Many nocturnal animals such as cats see quite well in the "dark," only it isn't all that dark for them. Night vision simply amplifies the light available. Inside a cave, after a few corners, there may be no ambient light to work with. That is why cavers don't bring along night vision gear.
I am not sure how great a flash bang would be in comparison to throwing a real grenade. If you are going to risk being close enough to through a grenade, why not make it one that will actually do harm to the enemy.
As far as grenades doing harm to the good guys as well as bad guys, caution must be used. As they discovered in WWII and in Nam, grenades can be used effectively in caves when there are major obstructions such as dual corners. In fact, the Cong specifically built such corners in to their cave system to shield occupants not in the immediate blast zone.
If one plans to go into a cave environment with noisy weapons, a definite piece of safety equipment needed would be muffs, ideally electronic muffs that would shield the wearer from hearing damage, yet allow the wearer to hear after the noise stops. Shooting in an indoor range with sound dampening materials on the walls is still much louder than shooting outside. Now imagine there being no sound dampening in a confined area composed of rock. Hearing damage would most certainly be a problem.