You should be able to do this by editing the system profile -> incidents -> create incident rule -> under conditions click add -> create measure -> Database monitoring. In that section you should be able to define a measure to track the disk metrics from Oracle.
Unfortunately, not. This data is not stored at all.
You may want to create a RFE for our Product Management to consider making that a feature for future AppMon releases. It seems useful for many customers. Please visit https://answers.dynatrace.com/spaces/151/view.html