The OP is pretty odd, if I’m gonna be honest!
Anyway, that’s some very good questions, and sadly there really is no easy answer at all. As someone who did roleplay them, my vampyr always hid their nature under illusions, that demon hunters & Spellbreakers could see through. If that happened, the San’layn I played would exit the premise hurriedly to not make a scene since prior to Battle for Azeroth, they were kill on sight.
Now… well. We don’t know. I use the logic: “We’re working with soul-drinking ‘vampires’ in the afterlife as heroes, and it’s not like that’s some big secret, so I feel like working with open San’layn isn’t that much of a stretch.”
I would say, maybe, they would be treated with a lot of wariness and even deep hatred, especially those afflicted by the scourge. They did show that there was at least a group of them wanting to finally have a home and fight for the horde (like Death Knights, and in Bfa), and we know they’re intelligent/have free will, so could make such decisions. I played my 'layn a lot like the mentality of Death Knights. I have an entire post on the headcanon I use for it since a lot is open ended.
All in all, I wish I did have a better answer for you. I guess I would say have your toon react as they would toward an ex-scourge, like if someone played a lich outwardly (which we do see in the ebon blade so would be viable). Probably not all too happy about them being there, but also likely not trying to butcher them flat out in the city AS LONG AS they are behaving well. In my personal opinion, if someone is playing a San’layn openly in the city, they’d better be behaving and very well, otherwise ICly you’d think they’d get slain by the guards.
I feel like in Silvermoon & Org, you could get away with more dastardly things on a Horde race that’s officially joined, but you have to be on your BEST behavior as something like a San’layn if that makes sense. This is due to likely being on such thin ice, but at the same time, we work with worse at this point, so would be permitted to at least be there an interact on good behavior.
Edit: I also roleplayed San’layn for YEARS and have a ridiculous number of vampyr characters. I still play them, granted, just in discord & with my guild. I was always someone to be super careful in cities, and I did play in them. My toons were hidden & on their best behavior. Nowadays it makes sense that San’layn would be more open, after all that’s happened, but they need to be super careful from my personal perspective. (This subject might be a good one to make a video on, I’m actually back to making videos again so who knows.)