I doubt that Procure is great for smolts, but I also bet that it leeches out of the eggs into the water pretty quickly. I don't see a lot of smolts floating belly up during steelhead season, which one would expect if Procure or Borax was immediately toxic. I'm not sure, but I imagine that the main ingredient in procure is probably sodium sulfite, which won't kill right off in small quantities.

As to how long the eggs keep, I have defrosted and frozen eggs as many as a dozen times and caught fish. It's not optimal, but they catch fish. Generally I freeze them if they're going to sit for more than a week in the refrigerator before I go fishing again. They'll start getting a stale egg smell when they start getting old.