Looks like they're not. From the Rolling Stone article: "the company will also take prescription details to build into the lenses for those who typically wear glasses."
That's not great at all if it means you can't share your headset.
It's probably because of the need to go to market quickly (a simple design helps) but I wonder if there is at least one founder of those companies that needs prescription glasses. Apparently all of them have perfect eyesight or wear contact lenses.
That's not great at all if it means you can't share your headset.