It doesn't look like it is throught the fiberglass, so the best thing to use is a gelcoat repair kit. If it has gone through the fiberglass, then you can use a epoxy filler first like the 3M premium marine filler.
You mentioned that an epoxy filler can be used and then gel coated if I'm understanding right. Is there a problem with the adhension of gel coat to the epoxy? I ask because I want to use a very low viscous epoxy undercoat(interlux epiglass) prior to applying gel to the boat hull. That epoxy will have to be properly preped before any additon coating is applied.