Short of depending on a borrowed actor concept from UT2KX, I've always dealt with this issue by using multiple lights. It's easier with Na Pali as a setting because the skyline is so rich with different colored sunsets and midday anomalies that you can have a deep vermillion dawn on the tip of the highest peaks around your canyon and balance the rest with other colors. Setting is of course important, but also scale. Depending on the map you are using and the size of your outdoor terrain, you'll have more or less options. Larger is always harder and you often have to balance lighting with the complexity of your outdoor buildings. So normal light actors for me have always been sufficient.
The sunlight actor is useful in concept, whether it be the one in 227, the one featured in the Uengine 2 and up titles, or a version included in some other Unreal project (RD).If your outdoor area is way bigger than Unreal intended, you might need one for sure. But I find that while it casts a big "master" light, I often end up placing normal actors around anyway. So for the reading impaired, the short answer is this; never rely on just one actor to make your skylight