A reader reminded me of FracFocus.org.
I understand that it might be a bit delayed in posting updates; I don't know.
Regardless, it can answer your question if you are wondering if a particular well has been fracked. The site is very easy to use; you do not need to enter the API number of the well if you know the name of the well and the operator.
The Bakken Shale Discussion Group has a nice thread on it.