We know that Google's stackdriver supports monitroing for third-party applications like postgresql, mysql, couchdb and others mentioned here. They have also defined the service configuration files for the monitoring agent here.
As per my understanding, I think they somehow use collectd's third-party plugins somewhere in this. Also, since there exists a plugin for Oracle, stackdriver should support that too. But I can't see Oracle in the list of supported third-party applications. So, does stackdriver support it or not?
The Stackdriver monitoring agent package does not bundle the oracle plugin, so it's not supported. You may be able to write a shell script (invoked via the exec plugin) or a Python script (invoked via the python plugin) to query your database, and the custom metrics mechanism to ingest metrics.
You could also try BindPlane from our partner, Blue Medora.
Disclaimer: I'm an engineer on the Stackdriver team.