As a biologist I have to speak up on this. THAT statement is entirely false, and speaks volumes about the amount of ignorance surrounding snakes in general. You're not the first person I've heard say this, unfortunately.
"Black snakes" (i.e. Black Rat Snakes, or less often, Black Racers -- 2 different but similar looking species) are oviparous...they lay eggs. Copperheads (and the rattlesnakes, for that matter) give birth to live young. These two reproductive strategies are COMPLETELY incompatible and it doesn't matter how many times they give it the ole "college try", they'd never, ever successfully reproduce. Don't believe me? The PA Fish and Boat Commission even addresses this on their website:
Frequently asked questions - amphibians and reptiles
Also, South Park addresses species incompatibility in their episode "An Elephant Makes Love to a Pig"....having them cross breed is just as likely as the situation above:
Link