Let me just humour this by taking the bait and telling you that there is no such thing as a half orc, all greenskin, orcs included, are sentient, humanoid, genderless mushrooms that reproduce through spores they release constantly, which is how they never seem to run out of troops- these spores always result in a combination of orcs, goblins, snotlings and squigs.
Therefore, an imperial human with bretonnian human lineage is completely possible, whereas a dwarf with orcish lineage is completely nonsensical. It’s not even an argument.