Electro's electricity is generated organically, even if he absorbs the electricity around him because it is stated he converts the electrons into organic energy in the Ultimate Spider-Man comic series. With that in mind, remember that symbiotes bonds to the hosts organic matter. They bond to the host's cells so much so that the symbiote eventually bonds with the their bloodstream (like with Carnage in the comic event "Maximum Carnage") and, in some cases, their DNA (which was what was stated to happen to Peter in the Spider-Man Animated Series if he left in on for too long). So, I don't think it would be too far of a stretch to say that since Electro is creating organic energy in the form of electricity, the symbiote would be able to bond to the cells that grant him this ability and therefore grant the symbiote to produce electricity with no ill effects (as well as absorb energy from around it).
Also note two more pieces of evidence; 1) Thor has struck Venom with lightning before in the Avengers comic when Mac Gargan wearing the Venom symbiote attacks the Avengers Mansion while part of the Dark Avengers, and this hadn't harmed the symbiote as severely as fire does, so it can be assumed that Venom is only weak to electricty in the Ultimate Spider-Man video game, the only time I have seen Venom unbond due to electricty. And 2) Venom has done the a very similar thing in the comics where he had bonded with Ms. Marvel and obtained her ability to fire beams of organic energy (seriously look up Ms. Marvel Venom on Google images and it will come up). And who else has organic energy? Electro. Venom even comments when he bonds with Ms. Marvel that "She's an excellent host! So full of energy!", implying that symbiotes are actually attracted to powerful organic energy.
Okay, remember this IS still a theory, BUT there is so much evidence pointing to symbiotes able to bond with a host that produces organic energy that it's a pretty factual assumption to have. Anybody agree with me?