I believe this is a die crack in an area that seems to be subject to them in this series. If you search the forum, there are a couple of nice pictures of 2007 shattered dimes showing a crack very similar to this. Here's an early stage crack on a 2007 dime in a similar position:
That wouldn't prove anything. A fingernail would catch on both a die crack and a plating issue. You can see a small "chasm" in some of the photos, and this wouldn't happen to a die crack. It would be filled. Chris
Doubtful, but possible. Blind-ended die cracks are rather common and they never seem to lead to anything more serious. The 2001-P dime shows a 50% retained cud and three additional die cracks within that retained cud. Together, they constitute a shattered die.