Brake12, keywords in captions do help the SEO traffic. Whether or not to have a title is a matter of artistic taste and totally up to you. I don't go overboard with keywords, but focus on what I want to emphasis in the caption describing the picture. I ask myself, how is this relevant to my article?
I've seen a lot of poorly written captions on Hub Pages, so you question is very helpful to other hub writers.
Information on image use: https://hubpageshelp.com/media/Learning-Center-leg (Note: Captions are used in the aritcle's images, but are not necessarily the best examples of effective captions.)