We have expected productivity requirements on a bi-weekly basis. The expectation is that if you finish 2 weeks worth of work early, then the next iteration you will get slightly more work. Of course this isn't 100%, (obviously someone could just take longer on purpose), but as a manager its pretty easy to tell when your direct reports are slacking off.
Personally I don't think having 2 salaried jobs is immoral. If you're not caught, I feel like it is indicative more of bad leadership than your skill. A good manager should know what someone of X skill level should be accomplishing. If you're only doing half of that, (assuming the other half was spent on another job), it should be fairly easy to notice.