Do I need any special drill bits?

No.  Just about any bit will drill a Kevlar helmet.

How large of a hole are you drilling? Typical metal type twist bits tend to leave you with a really fuzzy, indistinct hole in composite materials IIRC. A flat spade bit might cut cleaner but I've only seen them down to 1/4" size.

Installing a norotos universal shroud, so 3 small holes.

I think I remember from a previous helmet thread that folks had better luck with the bits that had little points on the outside edges, that those did a better job of cutting the fibers. I could be wrong.

DIY Helmet

Drilling for NV shroud

Info on making a FAST helmet and drilling for a NV mount.  Some people share their experience drilling kevlar.

A brad point bit works the best

Superglue helps too. Drill past the surface, seal with superglue, after it hardens drill a little more

For the small holes involved, I use your std high speed drill bits, slightly over-sized, then seal the edges with kevlar fuzz and a good 2-part epoxy.  After that dries you can lightly ream to size.  I don't know how big of a factor it is, but some guys get the vapors about un-sealed Kevlar to atmosphere.  Could there be moisture degradation?  Possibly but I doubt as much as it's talked about.  

I've noticed some slight kevlar fuzzing around the rail and suspension holes on older helmets and I don't think it effects the performance of the helmet.  But that's just me.  Other guys on here will tell you your head will explode if you do this, instead of buying a factory-drilled helmet.