Most snakes think geckos are the bee's knees. Including spotted pythons (if that's what you meant). In fact, a trick to get a snake to eat is to scent a mouse with a gecko. If a snake (perhaps by vine snake he meant the invertebrate eating 'green snake' from the US? Ahaetulla, the vine snake from Asia, is a lizard eater) was too small to eat the gecko, I would definately worry about the gecko eating the snake, as they're not too picky what they bite at. And then, after one eats the other, you have to worry about disease transmission. Not fun.