In the Blade film, Frost needs the blood of the Daywalker to awaken La Magra. Is it just a coincidence that Frost himself was the one to actually create Blade, and Blade was just a one in a million chance outcome, or was there more to it than that? Did Frost know of the prophecy and specifically target a pregnant woman hoping for the Daywalker outcome?
One specific plot device seems to say that Frost didn't create Blade just to fulfill the prophecy. Frost's Research.
Frost needed the computers of that specific time to finish translating and correlating all the information relating to the prophecy, in order to follow through with it and create the ceremony to awaken La Magra. He was still performing that research up until he performed the ceremony. So, he would have had to have completed that research in order to know he would have to make a Daywalker.
It is possible that he did research BEFORE the movie takes place, and learned of the prophecy, and that it would require a Daywalker, and then set out to make one... and then over time continued the research to learn what would be necessary to make the prophecy come true, however his modern attitude and the other vampires' reaction to him and what he was doing suggested that he learned all of this in short order.
Also, if he made the Daywalker just to take a specific place in this prophecy, he would have had a much heavier hand in the upbringing and life of Blade. He would have allowed his mother to raise him (instead of allowing Blade to think she was dead), and he would not have allowed Blade to become the vampire killer that he is. Blade causes Frost more trouble due to the events surrounding his birth and subsequent life than Frost would have normally put up with if he had planned this.
This is another time when the viewer must suspend disbelief and allow himself (herself) to accept what happens in that specific universe in order to follow along and enjoy the show. The movie was an action flick more than a logical piece of fiction, thus there are going to be holes in the plot. Yes, it's a big coincidence that Blade was the Daywalker Frost needed to make the prophesy happen, since Frost made Blade... but that is what it is.