His mother was an orc, so he was an orc. His father was a vampire, that's why he was a little pale. Not a hybrid

His father was actually an Imperial who turned into a Vampire.
This makes him an Imperial-Orc Mix.
And it has been confirmed in Notes on Racial Phlogeny that Mer and Men can bear fertile offspring.
After much anolysis of living specimens, the Council long ago determined that all ''races'' of elves and humans may mate with each other and bear fertile offspring. Generally the offspring bear the racial traits of the mother, though some traces of the father's race may also be present.
Considering how this comes from the Imperial University, I'd believe it.