As with any rule in the NFL, including the one that tells us what is and isn’t a catch, there are plenty of exceptions to the rule that says “character matters” when a front office decides to add a player to their roster.
Vikings fans are plenty familiar with exceptions to this rule. In modern history you can point to guys like Cris Carter, Randy Moss, Jared Allen, and even current Viking Everson Griffen as examples of young men that were able to overcome their early personal struggles to make a significant impact at the NFL level.
Despite all of those exceptions, however, NFL teams expend many resources to try and figure out what exactly exists between the ears of hundreds prospective players. The idea is that a player that is successful off the field is more likely to be successful on it.