Offsite housing exceptions are made on a case by case basis; because housing is an integral part of the Walt Disney World program, they would prefer that you are housed on property. The program at the Disneyland Resort in California allows offsite housing as a standard option.
On the other hand, Disney doesn't compel you to stay in housing if you pay rent. That means you could stay with your friends overnight at their place, or for an extended period of time without any waiver/exception, so long as you continue to pay rent (which is automatically deducted from your paycheck anyway).
I'll assume your asking in anticipation of applying for the Spring 2009 program - be sure to ask your interviewer about this during your interview.