The surveys are usually right if those surveyed end up coming out to vote. I guess the surveys can be wrong if the losing side in survey succeeds in persuading many of his/her fans to vote... This is probably why the surveys are important to politicians and their supporters.
Yeah but what importance does it have to gamblers? You are not given the information publicly or even if you are given by that time the betting time is over. You can talk about an exitpoll but that too the bookies are aware of and they will end betting much before the real election starts. So I would say its more of a speculation and luck based. Its is definitely possible that your supported member wins but the opposite is also possible.
This is why people should avoid betting on events. Its same as EV- games.