No, the 'Network proxy' setting configured under 'Configure Network' is not used for Cloud Access Manager proxy backend.
Any host that you want to reverse proxy with Cloud Access Manager has to be available directly from the Cloud Access Manager proxy host.
Note that the “Network proxy” configuration feature in Cloud Access Manager is only used for specific tasks such as Quick Connect Connectors for Provisioning to Salesforce for example.
WORKAROUND:
None
STATUS:
The following Enhancement request has been submitted to Development for consideration in a future release of Cloud Access Manager:
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TFS 784493 - Allow the Proxy to route *ALL* traffic via the Network Proxy
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