Hi, are you in the US? I am (Wisconsin), and I used to work at a blood donation center. One of the new tests we were validating (testing to see how accurate it was) was West Nile. In the hundreds of units of blood donated each day, from most of Southeast Wisconsin, they only ever found one person who tested positive over several years of testing.
Obviously an animal that is outdoors all the time will be more at risk. But I personally think that rabbits shouldn't be kept outside in my area anyway because of the summer heat and because I have heard of cases of rabbits with frostbite and a few even freezing to death. If your rabbits are indoors with occasional outdoor playtime they shouldn't be at much risk. I'm far more scared of bot flies and fly strike than West Nile Disease.