Regardless of whatever influence the morphic field may have over humanity, Jack immortality was an effect of the time vortex itself, one of the most powerful forces in the DW universe. The Doctor said it made him a fixed point in time. Though he had to be biologically "alive" for this to happen, there was nothing inherently biological about the immortality.
So, I guess 2 questions:
1) Should the morphic field be able to overwrite something as overwhelmingly powerful as the time vortex?
2) How could Jack's blood have caused any of it when this trait wasn't biological, but caused by space-time?