What I have personally wondered would be, what is the vector for the seeding? I've always thought it had to be a retrovirus of some sort, something programmed to be extremely stable and maintain its code over billions of years so that it can repeatedly guide the evolution of the target species...in other words, one HECK of a technological accomplishment. Especially
when you consider that we've seen it work on mammalians of varying biochemistries (humans, Vulcans), therapsids (Cardassians), reptilians (Voth), and other forms entirely.
Whether this is actually feasible or not, I'm not sure and rather doubt, but it's the only explanation I can come up with in the context of the Star Trek universe.