Yes, an IT Policy will persist. They are designed NOT to be removable by the end-user. About a year ago, RIM released Unite, which was supposed to give BIS users BES-like capability. Instead it gave them IT Policy nightmares. I think Unite has since been fixed. One good outcome was the development of user tools to remove an IT Policy. The best one to my knowledge is here:
Removing an IT Policy from a BlackBerry phone. Try it, and see if it will allow you to delete the IT Policy and then turn off Memory Cleaner.