I've already worked out some interesting spirit sensing stuff with Urahara. So I'm sure we could work something out here as well. Honestly, canon also had Korra fairly powerful spiritually in her own right. But when you have a big spirit like Raava in tow---well those attuned to it could likely pick up something even if they aren't sure what it IS.

And then on the Jason front...that sounds like it could make for some interesting conversations! Cause that is not how demigods work in his world XDb