Honestly, I don't know enough about making fish food from scratch to know exactly what kinds of vitamins they would add. My guess from reading the article is that he's added some kind of over the counter adult multivitamin sort of thing. (As opposed to Flintstones, which has all kinds of dyes and flavorings added.)
Quite frankly, and this is completely my opinion, I would be concerned with adding a general vitamin supplement without knowing what kind of vitamins/nutrients the fish actually need. Even though I feed my fish peas, zucchini, and romaine lettuce (I have a pleco), I sometimes roll my eyes thinking about how often fish encounter zucchini in the wild!

Of course, what we are trying to do is to give the fish access to the same/similar sources of nutrients as what they would find on their own, but still it makes me laugh.
If it were me (again, this is pure opinion), I would skip the vitamin step completely and feed some sort of high quality flake or pellet food in addition to the homemade food. I'm not saying to feed the commercial food continuously, just to use it to supplement the fresh food you're making. Chances are, your fish are getting much of the nutrition they need from the fresh food. Also, chances are that Hikari has a much better idea of what vitamins fish need (and in what doses) than you and I (or the Flintstones people!) do.

Just my two cents.
As for the frozen bloodworms, my guess (again, just a guess) is that you would have to re-freeze unless you were using it inside a few days/week. Eventually the bloodworms would spoil. It's probably safe to refrigerate for up to a week (although if it started to look/smell funny -- funnier? -- I would toss out that batch), but frozen foods will spoil eventually if not kept frozen. Again, just my opinion. I believe the gelatin/agar could be frozen with no ill effects; I don't think the freezing process would cause it to break down, and its primary purpose is as a binding agent, I believe.
Take this advice as you will. My opinions here are based more on cooking and dabbling with natural cosmetics than anything remotely related to fishkeeping!
Good luck,
Pamela