Yes. Apple will replace the back with a brand new (unscratched camera lens) for $30. Its quick and easy I had this done myself
Getting it replaced at Apple will work or you can search eBay for different colored or patterned backplates if you want something different. I've ordered an aluminum one and a white one and both have worked great.
Usually when this issue happens with the scratched camera lens you will never see the scratch in the pictures that you take.
The scratch shoudnt affect your picture quality at all. This was a top on here some months ago and there was a link to a person who tested this theory, using a shattered fish eye lens next to an un shattered, almost impossible to tell difference in quality. This isn't the one that was presented, but is still interesting. http://www.petapixel.com/2011/06/16/how-dust-and-damage-on-lenses-affect-image-quality/
I dunno, I think it depends on the severity of the crack. I don't have a picture, but when the glass in front of my HD2 camera spiderweb cracked, all my pictures started turning out foggy. They used to be crisp before the crack. I removed the cracked glass and my pictures look perfect again. EDIT: Alright, so I don't have a before and after picture to compare the pictures with the cracked and without the cracked lens, but this is the foggy effect I was talking about. The picture with the green Xbox beta disc was taken with the cracked lens. It looks unfocused and foggy. The picture of the Roasters napkin was taken after removing the cracked camera glass. The picture looks fine now.
Mine was scratched pretty bad (not just a single scratch) that it left pictures noticeably blurry. I went in to pay the $30 for a replacement back, but they did it for free under warranty.