In 2009, quarterback Michael Vick, then a member of the Philadelphia Eagles, was 
placed on the exempt list after serving a jail sentence and suspension for his participation in an illegal dogfighting ring. Similarly, former Tampa Bay Buccaneers safety Tanard Jackson was placed on the 
exempt list in 2011 after returning from a year-long ban for violating the NFL's substance abuse policy. Former New Orleans Saints linebacker Jonathan Vilma spent time on the list in 2012 after a suspension for his involve in that organization's "BountyGate" scandal, though his stay was 
health-related. However, both Vick and Jackson were allowed to practice while on the exempt list, which indicates that the Vikings made the decision to ban Peterson from practice.
The exempt/commissioner's permission list isn't necessarily reserved for troubled players. The Buccaneers placed running back Jeff Demps on the list in 2013 during his pursuit of an Olympic track career, 
Deadspin notes.