Actually, looking at my Physics book, it lists silicon as a Semi-conductor, something that can carry a decent current. Other minerals probably have similar properties. I highly doubt that Gaara's sand would completely stop an electrical current from flowing through it. Remember that any user of an akuma no mi has their body composed of the element that they are the user of. Since sand is not a super resistant, like rubber is, even if it did manage to hit Eneru, it probably wouldn't do any damage to him since he could always become electricity. Also, we have to look at the fact that akuma no mi users can use their abilities endlessly. Unless they sustain damage, there isn't much of a way to stop them. A shinobi like Gaara can only use his abilities so many times before he runs out of chakra. The amount of electricity that Eneru uses is enough to floor Gaara if he's hit even once. I say that Eneru wins.
EDIT: I also forgot to mention the speeds at which lightning travels. If Gaara's sand could not keep up with, say Lee, a mere human, then how could it hope to keep up with the speed that lightning travels. It can go very large distances in a very short period of time. More likely than not, the sand, would have a very difficult time keeping up. Also, the length of the sand would be very short, while the crossarea of it would be very large, which only decreases the resistance. Like I said, I believe that Eneru wins, but it could also be a tie. I just don't believe that Gaara has what it takes to beat Eneru.