I'd be very skeptical about this. The "explanation" proffered is that human tissue carries a negative electrical charge, snake venom carries a positive charge, and the two attract; application of electrical shock reverses the charge on the human tissue and repels the snake venom. I don't believe I've ever heard that human tissue carries an electrical charge, or snake venom either. Even if the theory were true, applying electrical shock to the area around the bite would then, logically, push the venom deeper into the body, causing more harm than good.

According to a BBC article online:

Electric shock therapy has also been found to be ineffective at neutralising the effect of venom, despite its widespread use in Africa and South America.
(http://news.bbc.co.uk/2/hi/health/4498779.stm)

I thought this one was a "Darwin award" urban myth, but apparently it really happened:

Dart and Gustafson described in detail the case of a 28-year-old man who was bitten near his right upper lip by his pet Great Basin rattlesnake (Crotalus viridis lutosus). The patient had been previously bitten 14 times. During treatment for 1 of these 14 bites, the patient had experienced an anaphylactic reaction to antivenom. On the basis of information they had read in an outdoorsman's magazine, the patient and his neighbor developed a plan to use HVDC shock treatment in case the patient was bitten again. The patient and his neighbor were provided with the opportunity to test their plan after the patient's 15th rattlesnake bite. The snakebitten patient was placed on the ground close to the car. The HVDC shock was delivered by attaching a lead wire from one of the car's spark plug wires to the patient's lip. The neighbor then started the car and revved the engine to 3000 revolutions per minute repeatedly for approximately 5 minutes. The patient reportedly lost consciousness during the first HVDC shock treatment. The ambulance crew, who arrived about 15 minutes later, found that the patient was unconscious and had fecal incontinence. On the basis of the ambulance crew's initial evaluation of the patient's unstable vital signs, he was transported to a hospital by helicopter. The patient arrived at the hospital approximately 1 hour and 40 minutes after the bite. In the emergency department, the patient was found to be obtunded, hypotensive (blood pressure 62/palpable mm Hg), tachycardic (pulse rate 120 beats/min) and hypothermic (35.4°C). The patient experienced severe face and neck swelling that necessitated nasotracheal intubation. After fluid resuscitation therapy, the patient regained consciousness and vital signs stabilized. Laboratory testing revealed moderate coagulopathy (protime 20 seconds) and thrombocytopenia (<40000 mm3) that resulted in the administration of 10 units of platelets. The patient exhibited a positive skin test reaction to Crotalidae polyvalent antivenom and received hydrocortisone 200 mg, diphenhydramine 100 mg, and cefazolin 1 gm intravenously as antivenom pretreatment. During the following 8 hours, the patient received 27 vials of antivenom. The patient was discharged after a bout of serum sickness with residual facial edema and loss of facial tissue, which ultimately required surgery. (36. Dart RC, Gustafson RA. Failure of electric shock treatment for rattlesnake envenomation. Ann Emer Med. 1991;20:659–661. Cited by Wilderness Medical Society:
(http://www.wemjournal.org/pdfserv/i1080-6032-012-02-0111.pdf )

The authors of the article, following a review of the available medical literature, concluded "that the use of stun guns or other
sources of high voltage, low amperage direct current electric shocks to treat venomous bites and stings is not supported by the literature."