as for me, i was stung/bit by a huge RED HARVESTER ANT (these are 5 times bigger than the venomous red ant) on the top of my foot in the sonoran desert, my foot swell up and i felt the venom traveling up my leg, throbbing pain, this went on for 2 hours and i was getting worse and worse and had to lie down. i thought i was going to go to a hospital but we are so far away in the desert and i don't have insurance anyway, so i decided to use my zapper (i have the ULTIMATE ZAPPER made by Ken Pressner), i put one handheld in my sock near where i got bit, and the other in my hand. in EXACTLY 19 minutes all throbbing and pain and swelling STOPPED and i got up and fixed myself lunch.
what i understand is that the electrical charge changes the molecular structure or somehow just neutralizes the venom.

as for more powerful venom like a rattle snake, well, many hikers carry 9 volt batteries in case of snake bites; the translators for Wycliffe actually sell stun guns for their missionaries out in the field for extremely venomous snakes, in Mexico sometimes they use car or motorcycle batteries.
the "medical" "scientific" studies on this has not given good results because they use mice as "testers" in a funky lab setting and have never tested it on humans. However, those humans who have used electricity swear by it. for bee stings too.
personally i know for a fact it works on the HARVESTER ant of the sonoran desert (they are about 5 times BIGGER than the red ant.
i was amazed.
photo: HARVESTER ANT seen next to regular sized ants for reference
http://www.alexanderwild.com/Ants/Natural-History/Ants-fighting/i-hfhmWKW/1/L/maccooki4-L.jpg