I agree with Orin about not mixing differant Genera together.
Although i had a friend who had B fusca and decided to throw in discoids with them.
One by one the discoids disapeared untill there were none left.
This friend may have been neglectfull with his feeding duty's.
I think as long as they are well fed, you should have no problem.
Most people who keep roaches, usually feed them well.
Although prosticus are known to devour other small insects when hungry.
Have you ever had this experiance Orin?