Hi Matt,
No one to my knowledge has tried to hybridize hissing roaches. It would be a a very interesting thing to do, however!
You would need to separate females of each of the species you wanted to hybridize from any males when the females were still large nymphs. You would then need to rear them to adulthood, introduce males of the 'other' species you wanted to cross with them, and see if any nymphs appeared in a few month's time.
Cheers,
George