Gelatin setting has nothing to do with freezing so the freezing point of vodka is irrelevant.
Gummy bears are "firm" because they contain gelatin, just like jello. You can think of them as really firm jello. How "hard" they set up depends on the ratio of gelatin to the liquid. That's why gummy bears are firmer than jello, their gelatin to liquid ratio is higher. When you soak gummy bears in vodka the vodka "dilutes" the gelatin, so no, they won't set up as well as un-soaked gummies would.