In the regular cut, the voices are fine because The World Between Worlds has already been established but any pre-OT Jedi coming back as physical ghosts doesn’t fit with what we’ve seen (excluding Qui-Gon and possibly Ahsoka).
Interestingly enough, the novelization pretty much flat out tells the reader that the voices are coming from the World Between Worlds. Which does mean it’s different than Force ghosts. More has to do with potential realities, pasts, and futures.
Didn’t remember this and just checked:
The battle above disappeared. Instead, Rey saw a perfect sky, vast with stars. Peaceful. Light-filled. It was like she was staring through a window to somewhere else, a place between places.
…
More voices came at her fast but gentle, as though she lay at a confluence of the Force, possibilities, futures and pasts all stretching away with her, or maybe leading toward her. The cosmos, time, energy, being- nothing was the way she’d thought it was.
…
Presences filled her aware, some recent, some ancient, some anchored to the living in a strange way. Rey didn’t understand. But she accepted.
Huh. So not only does it basically say this is through the World Between Worlds, but the interesting part is the “some anchored to the living” part, which to me clearly seems like them keeping the door open for Ahsoka to still be alive. And if they later decide she’s dead by this point, that can just be taken as being from another Force sensitive at the time. Ezra? Who knows.