Assuming that you'll never land from a jump with your pedal down on a rock, then there is not problem.
On the other hand a little protection doesn't hurt. Maybe you can get those end plugs from CrankSkins. My race face sixc cranks had similar ends on. After riding hard for 1.5 years there aren't any serious dents and dints on them, but again, more protection does not hurt.
A more sensitive area though is that one bellow your feet (when riding a trail with your feet level). These are not protected by default (in my sixc at least) so I've taped a slice of inner tube using a strong double sided 3M tape at the correct places (keeping in mind that I always ride right foot forward).
Scratches are not a problem I think. What can be problematic is hitting rocks with the cranks. I don't have experience cracking one though.