As I play a Morninglordian. I'll speak up a bit
For as long as I can remember, the Faction has never discriminated since even in the dogma it states there is goodness in evil hearts, just as there is evil in good hearts. Its their job to guide to the light.
In the beginning, there were Morninglordians who would chase the Calibans out, but DMs corrected the members stating that all (Undead excluded of course) were welcome to seek shelter in his temple, with the understanding that trouble was not to be caused within the temple.
"Tieflings" are still human, with demonic ancestry. So it is unlikely they will immediately go "EVIL!" if there is a possibility said Teifling could have some good in them. And in my PCs experience, she has dealt with a deceptive teifling that tried to destroy her marriage, as well as one who while not discreet has aided against the churches enemy. But basically, yes the faction is a goody good faction who is forgiving. Heck, when someone stole from the church the NPC said "They must need it more than we do" and forgave the theif.
That being said. Yes, I think parading around exposing the hooves and horns and whatnot is kind of ignoring NPCs though, because the temple IS visited by barovian/gundarakite believers, so such a sight would cause a panic and the NPCs would have to react to that. I know it happened once before, where Ehliel exposed her wings and the Light Carriers quickly escorted her out of the temple. However she was welcome back in when she learned discretion.
But even in the canon book, it states while rare, there can be good aligned Tieflings, just as there can be evil aligned Aasimars. Just depends on the history/upbringing.
As for the O.P. I don't think there are too many areas perse, cause if there were less then there would be less exploration which is also enjoyable, but a matter of time of travel. I know I tried to make one of those Hotspot things, but by the time I got to the Vistani Camp, travelled the 6 min between to get to the location, it was either over or just didn't happen cause no one was there.
I think this Hotspot is a good idea, if it can draw PCs together (With good IC reason) to which they can then plan an expedition.