I think there are different terms but I'd call such a person a licensed venomous reptile handler or a herpetologist though the latter is more involved in the study of the snake's behaviour. There are also plain old snake charmers who tend to obtain the job by virtue of it being "in" the family.
Seriously though, snake venom is highly coveted by researchers (like me even) because it is used in the manufacture if many diverse medications. We tend to call the people who milk the venom venom extractors or just plain snake handlers. There is an ongoing study involving snake venom that is showing impressive results in the treatment of cancer. Certain snake venoms can stop or interfere with blood-vessel formation in tumours so we'd like as much of it as we can get!
I am not personally afraid of snakes - I have one who suns himself on my front step and I call him Snavily. He crawls out of whereever he hibernates every summer like clockwork - and LOVES heat! However, I am not yet ready to donate him to a venom lab - he seems to like the neighbourhood too well and we all give him his space. He even watches me mow the lawn, lol (and I always watch for him before we do the lawn!)