When a proxy is set, does the functionality route timesheets to the person designated as the proxy for a supervisor responsible for timesheet approval?
Resolution
Whether someone is set up as a proxy or not, to approve a timesheet you need the timesheet approval right for the instance or the global approval right. The exception to having these rights, is if you use a timesheet approval process, then you are approving an action item, which would not require the approval right.
The notifications mechanism that is built into the timesheet module doesn't use action items, so it cannot take advantage of the proxy capability (since proxies only apply to action items) The manual timesheet approval functionality does send a notification to those who have approval rights over the resource who submitted the timesheet, however the notification itself is not an action item.
Proxies can be used in timesheet approval, if your site uses a timesheet approval process. Most timesheet approval processes, by default, will generate an action item for each of the assignees of the timesheet process instance. (You can look at the Project Manager Approval process as a start to see how an automated timesheet process can be set up.)