A keeper I know was bitten by a captive bred Puff Adder...believe me when I say the venom from that thing was every bit as bad as it's wild counterpart! He had a very bad reaction to the anti venom and spent three days in hospital on powerful antihistamenes via an IV!
He's a very experienced keeper and has many, many, many snakes including Mfezi's, Rhinkals, Gaboon Viper, horned adders and the like. He breeds them and rescues them, and a few of his snakes have featured in films and doccies!!!
i agree that captive hots are every bit as toxic as there wild conterparts. and i would also agree that if i had to choose that a bite from a wild speciem would be a "better" situation, simple because most bites from captive animals are feeding response bites and are there fore far less lickly to be dry.