I don't agree.
Their mandate was to investigate high-level fraud and that was part of their training to be higher-level civil servants. They, if they were successful, become prefects, administer occupied territories and were also assigned special missions. Some of them served with the armies. One was given the high-level posting of managing Napoleon's Bureau des renseignements and one actually became Augereau's chief of staff in 1814.
I don't see Napoleon creating a group of civil servants with considerable authority and then having them do nothing. That wasn't his way of governing.