Can you shoot down nuclear projectiles mid-flight?
Yes, you can shoot projectiles and grenades using V.A.T.S..
You can even shoot the mini nuke carried by suicidal Super Mutants as they're running towards you as an easier method of killing them, but as it's probably better to kill them without detonating the mini nuke so you can loot it!
You can shoot the Mini Nukes that Suiciders carry, and you can shoot thrown grenades, but sadly, you cant shoot Mini Nukes out of the air, so, no saving yourself once its been shot.
Edit: Just saw the date you posted that lol.