Can epoxy/primer still rust?
 

I'm really paranoid about this tiny little spot on my car's front right fender

Anyway, back in the summer some douche's car rubbed against mine pretty badly, the little scratches were buffed out but this particular area still remains untouched

http://i13.photobucket.com/albums/a2...81104-0922.jpg

I took it to a bodyshop and they told me there's still a layer of epoxy over the metal, it looks a little gray-ish white in the picture, but its actually a very dark grey in real life.

Can that still rust? I will be getting touch up paint asap from the dealership
I've also read that wet sanding is necessary for a good touch up job, but since this area is not really as
visible as other parts, is that really necessary?

Anyone have any tips? Is it still possible to do a decent job without sanding or will it just
look like ass?

The primer used my most maufactures won't rust, but it's going to vary from paint-to-paint.

Most of the time though it's not the primer that rusts, but that the primer is so thin the metal rusts through it.

Sanding is a must.