Filter users in views with a mandatory role and another role that is optional
You can put condition in View's criteria. 


Go to your view and step ahead to filter. 
Put first filter as. For example you have role as category A and category B.


Add following filters which can be helpful as per your scenario.

   Select content:role (condition : is one of A and B)
                    OR  
   Select content:role (condition : is one of A)
                    AND  
   Select content:role (condition : is none of B)



Don't forget to add OR and AND condition in between filter fileds.


Hope this will be helpful.