If your app has a minimal front end but lots of back end calculations, you might consider the Unit Testing module. It allows you to define and run tests for your microflows that you can then audit and export. This will enable you to produce a record of tests that might meet your Audit needs. You will need to build tests for your microflows, but if this type of testing is important then it might be worth your time.
For your first question:
ATS tests apps based on the GUI. So, with integrations ATS also needs the GUI to be able to test the app. But as long as there is a GUI that shows the results of what you want to test it is possible.
For the second question:
ATS has a report functionality, with which a PDF report is produced containing the results of all your test scripts and their execution date. It is on the roadmap to customize this report to your preferences. The PDF report function is also possible for your test scripts, giving a detailed report of the test script and the steps it takes.
I hope this helps!