Yes, most pool lights can be wired with water in the pool. Almost all of the common pool lights are wet niche lights, so the fixture is completely surrounded by water and there is water in the conduit. These lights are normally wired before filling the pool on new construction, but installing them wet is how you handle things when the light fixtures need to be replaced. The conduit should be water tight and the other end should be well above water level, so there won't be a leak unless something breaks.