Hartshorn is very good, but there are very real people who believe he is not a corner OF'er. And at that point, it's a 1b prospect. I like Hartshorn a lot, but at 1b, this is not as premium of a prospect as it seems if he plays RF.
Then you have to remember this: if the Cubs are trading Hartshorn, the return will match it. I would assume the other team definitely sees him as a COF in that case and the names would be at the very top of the available names if they did.