I think so. Someone with better knowledge of the WOJ (Serack/CuriousFan) would know better but iirc to be starborn you had to be a wizard/witch and be born at a certain time of year and in a specific year. Harry and Elaine both fit into these qualifications.
As for it granting immunity, I believe it does otherwise Harry would've been infected when he was 16 and if Justin was infected he wouldn't have needed to enthrall them, just infect them. Also the Outsiders that Harry has met have attempted to recruit him, not kidnap and infect him. That being said I do believe that Elaine may be working for the other side. If they attempted to recruit Harry logically they would try to recruit her as well. Also the amount of trust that both the Gatekeeper and Mab place in Harry allows them to be fairly positive in his allegiance and from before they really knew him as well.
Others who are definitely not infected: Mother Summer and Winter, same reasoning as Mab and Gatekeeper, if they were infected they would have enough power to destroy the gate. Also Titania, for similar reasons as if she were infected she would have full blown attacked Winter and at the very least weakened Mab giving the Outsiders their opportunity to break through the gates.
Angels, Archangels and God aren't because of the above reasons. Sanya for being a KotC. Drakkul, Ferro, and Odin. Really anyone with a payscale big enough to go head to head with Mab and be an actual threat to her.
Edit: Forgot the scene with Maeve talking about taking Justine to get to Lara. Although it could just be a front trying to get Harry, Mab and crew to trust Lara.