Google GSuite Securlet has the capability to include Google Keep activities as well. This article goes over the steps to configure a content inspection policy for Google Keep on DLP Enforce.
It's a three parts process.
1) Policy Group
Choose a policy group or create a new policy group to be used for the "Google Keep" Securlet policies
2) Define an Application Detector
3) Policy
4) Verify that the modifications on the application Detection is Sync'ed to Cloudsoc/CDS
5) DLP incidents will look like this:
Note: Adding "Google Keep" to the predefined list of Securlets in DLP Enforce is in the roadmap.