Brian; Project, by design works in hours. If you enter a task of 8 days duration, the assigned resource automatically gets the appropriate Work hours assigned. For example if the resource were assigned the task at 100%, a value of 64 would be placed into the Work field automatically. (8 hours/day * 8 days).
In our organization, we primarily use the default timesheet, but we’ve also created another timesheet version that allows the resource to update the Remaining Work field. I’d suggest cloning the current PWA enterprise timesheet view and adding the desired field(s) such as as %Complete, % Work Complete, or Remaining Duration to the new view. Then configure the view to allow the timesheet user to update those fields. Then submit the timesheet and see what happens, so to speak. Obviously, you’re doing this in a test environment.
Personally, I’ve never played with sending in timesheet updates with no hours, just task field updates. But it seems logical that if I can update the Remaining Work field in a timesheet, I should be able to update other fields as well.
I wish I could provide a definitive yes/no that it will or will not work.