Add iPhone shutter count and serial number to EXIF data At present neither shutter count nor the iPhone serial number are embedded in iPhone picture metadata.

Is there an app for that?

Reason:  Pictures come into a database from multiple sources.  Using the date/time stamp already gives collisions due to camera burst mode, and multiple photographers.  I would like to assign each incoming asset an asset number composed of model+serial number+shutter count.  This generally works for mainstream cameras, but it doesn't work for iPhone.  Is there an app that would add this in automatically?
No, Currently there are no apps which would be assigning shutter count / serial number etc. Apps like that would have to keep on working on background and then edit Metadata of photos. On iOS, editing photo would need user's permission and would trigger an alert view saying "Do you want app to allow modify the photo" etc.
So, creating such app is technically impossible on iOS without Jailbreaking. 

Also note:
There are apps like "EXIF Viewer by Fluntro", which allows you to view shutter count of photos you took on Nikon Camera etc. It also allows you to edit exif tags like Camera model, software etc.

Disclaimer: I have developed the EXIF Viewer by Fluntro App :)