You make good points, but, again assuming the same rules as real world science applies, I have a hypothesis. A sperm cell and egg cell are, compared to other human cells, half a cell. By comining, they make the full cell that is a zygote, which replicates etc. etc., you get it. Perhaps the half-cell of Lovidicus' sperm was not enough to give vampiric traits to the mother, but enough to give some of their strength, speed and physical traits to the child? I guess unless more half-vampires start being born, we won't know for sure. It would be easier, as well, if the fathering vampire was a redguard or Dunmer, to acertain where the paleness came from.
A sperm cell is a complete cell, just as an ova is they meet, mate, merge, then divide based on the codes within each that tell what should be dominent or recessive. There are no half cells involved in procreation. But if vampirism is just a faction, and he is listed as an Imperial, then what Lord Lovidicus donated to the mix would be his Imperial bloodlines (IMO). This can be proved because there are no "half vampires" in the game.
@ Syronj - I think what keeps the offspring of mixes between man and beast sterile is the differences in the skeletal structure and metabolism between the two races. - The Gray Prince was the spawn of a vampire, but not half vampire - BTW, I have been dying to read Loranna's Lore RP, Rumple was saying something about it last month - can it still be found on here?