Once again, your headshot is supposed to be an accurate representation of what you really look like. While a good makeup artist can help hide your flaws, accentuate your features, and can be a vital part of a photo shoot, a headshot is not a “glamour” shot. You should look good, but without looking like you are wearing makeup. So, if you feel the need to hire a makeup artist, make sure you stick with “natural” looking cosmetics and keep away from heavy doses of eyeliner, eye shadow, lipstick, etc.
Something else to consider: if a casting director chooses to review you after seeing your headshot, you should make sure that you actually look like the person in that headshot. If you think you need makeup but can do your own makeup, you probably don’t need a makeup artist.