There was a big thread about this when Dark Ranger customisation first became a thing. You might want to scroll through it, just to get a feeling on the different opinions.
https://eu.forums.blizzard.com/en/wow/t/dark-rangers-in-stormwind-city-rp
In the end, there are two different schools of thought regarding Dark Rangers.
- There is no official lore directly stating that undead Night Elves have been accepted by the Alliance or the Night Elves, therefore they haven’t been accepted by the Alliance or the Night Elves, and anyone who plays an undead Night Elf and roleplays it as being a part of the Alliance or Night Elven society is breaking the lore. It’s that simple and until Blizzard produces new lore, all undead Night Elves are enemies of the Alliance.
- The same quest that unlocks undead Night Elf customisation mentions that some of these undead Night Elves are looking to return to their own, if Tyrande would have them. Moments later, you’re able to create Alliance characters that are undead Night Elves. Therefore, it seems likely that they have been accepted, because why would Blizzard give a faction customisation options for characters that aren’t allowed in that faction?
No matter which option you choose, it’s probably for the best that you stay out of cities if you play an undead Night Elf. No matter what the lore is regarding undead Night Elves in the Alliance, people are free to roleplay their characters as being hostile towards them.
This unfortunately means that you won’t be able to participate in hub RP, but at least it’s better than having to constantly deal with people trying to kill your character or have OOC arguments with you over the validity of your character’s existence.
We will never know for sure until someone is able to get Blizzard to clarify this issue, which might take many years or never happen at all.