No, if a guest chooses not to share their email, then a random Apple email address is created. See Why/When the email address of a loyalty guest is something similar to "<unique-alphanumeric-string>@privaterelay.appleid.com"? If the guest chose not to share their email, then they had the choice to forward emails to an email associated with their Apple ID so they will still get emails there.
Guests will not be able to change their email from the app if they chose not to share their email but may be able to add a secondary email. Admins can change the guest email by following How to edit a guest profile? but when the guest signs back into their account via Apple SSO, the email will revert to the random Apple email. The admin can add a secondary email to the guest account but it may not be visible in the app if there is no field for a secondary email.
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