First of all X, Carrie was not a belmont. Although, I do remember something about her being a relative of the belnades family. So, perhaps she is Sypha's great great…..niece.
As for Dracula (or any vampire drink the blood of a belmont), it could be beneficial or detrimental. Going back to a theory I mentioned on this forum several times, I've theorized that after the ritual that completed the vampire killer in LoI, Leon became part vampire (or at least gained some vampiric power). This is why they can use the vampire killer with no side effects and also why they are stronger than most other hunters. I also heard in CoD that after being stabbed by Issac and rescued by Julia, Trevor got up and left the next morning (something no human could do even in modern times). The fact that they wield holy power means nothing. I mean even Alucard could wield a cross and perform the grand cross crush in SotN.
That being said, if my theory is accurate, it would depend on what happens when a vampire drinks the blood of another vampire or someone with vampiric power.
(by the way, several people on this forum have stated in the past that I may be on to something with my theory.)