I've been using white pigmented epoxy on paddle tips, but I don't think I use in on a boat, for one reason: weight. In order to get it to be opaque, you have to apply it quite thick, which would add considerable weight to the boat. You would also have to apply it in several thin coats, in order to avoid runs. Paint would be a lot lighter and easier to apply.

Additionally, although the pigment should protect the inner layers from UV, the outer surface would still be subject to UV degredation unless you apply paint or varnish over it, adding more weight, expense and work. All in all, it seems like more hassle than it's worth.