no i wouldnt care if they were night elf and blood elf only because i would make a blood elf demon hunter anyways, but the lore is that any race can be one. nothing needs to be changed or made up, any race that is willing to use fel magic and could convince a demon hunter to teach them could become one, its not like light magic, or nature magic where the entire race doesnt even use it or even know about it.
the magic demon hunters use isnt foreign to humans or gnomes or dwarves ect they are open to and use fel magic, its the way demon hunters apply and use them and their rituals which are different, not the magic they use.
the difference between a human demon hunter and a tauren paladin is that previously tauren never used light magic, humans already use fel magic all they need is to convince a demon hunter to teach them how to use it a different way, same way monks are a class, we already had warriors and rogues, monks were just another class that fought, but in a different way