drop bear
Sr. Grandmaster
This falls into the same category of assumptions as the ones made by strikers that say they don't have to worry about grappling. Although MMA fanboys like to ridicule the "I won't let him grab me" argument, when asked about shots to the groin/eyes/throat they say "I won't let him hit me there". Well, it can work if you have good instincts (and you're better than your opponent) but it's still pretty unsafe to think that you'll be able to defend against something you never encounter in your training. In a competition you can be surprised by a hit coming from an unusual angle, I think that a fortiori you can be caught off-guard by an unusual strike to a prohibited target (like someone clawing at your eyes). Moreover, one might say that you can develop bad habits that might leave "holes" for those prohibited moves since they are never used in competition (it's along the same lines as why grappling supposedly isn't suited for armed encounters or multiple opponents), even though I'll leave this point to someone who has better knowledge of MMA.
No. Wrong way of looking at it. If you can strike more effectively than the other guy. You have a better chance of delivering eye strikes and groin shots and resisting theirs than if you can't strike effectively.
So it is not the case of a fighter being immune to those shots. But more the idea that they re doing everything they can to prevent it anyway.
For example say I was deeply concerned about being eye pokes while trying to punch a guy. What exactly would I do differently?