Yep! Anyone who's on Retrospec can see and hear him at least somewhat due to the resonance world change thing, but he'd probably be kind of transparent and not quite there... but if they can generally see spirits and stuff, then he'll be completely visible/audible/opaque/etc!

Also there was a Thing in November where a bunch of dead people came back and were semi visible to everyone, even people not on the app, and they gradually became more and more real/alive seeming throughout the month before they all moved on, and that happened to Jamie as well—ordinary people started to see him again, and things went more and more back to normal until December hit and he was 100% invisible again. ¯\_(ツ)_/¯