DEVONthink and Scanner Pro for iOS have both been updated in the last week to provide better integration between the two apps. Now Scanner Pro shows DEVONthink prominently as a destination app for saving scans.
The implementation isn't ideal though. It's only marginally better than using the "Open In" function and importing into DEVONthink. I would have loved to see DEVONthink as a location for automatic uploading from Scanner Pro.