Yes, you can. However, you'll experience the same problems you get lightening a dark picture. You'll have increased noise levels. You won't be able to get detail from areas that were totally dark. You'll having banding problems with areas showing gradual changes in brightness.
If you're just trying to boost brightness a bit, it shouldn't be a problem. If you are working with really underexposed video (more than a full stop underexposed), you're probably not going to be happy with the results.