Have you checked out the NTA The specified item was not found. thread? It has some helpful information in it including a link to a thread on Configuring Cisco ASA for NetFlow Transport.
I have actually configured the both devices without any issue, my question was more from a design perspective.
Since both devices are in the same location/subnet, is there any value in getting netflow data from both devices or is it just extra data at that point?
I believe the answer is "no there isn't any value" but I wanted to confirm that. :)