Can a cleaner sign in without an email address?
Yes: add them with a mobile number and they sign in with that and a PIN.
When you add a cleaner in Setup → Team (or at sign-up), leave the email empty and fill in their mobile number. They sign in by typing their mobile number in the Email or mobile number box, then their PIN.
Each mobile number can only belong to one active person in your company. Office staff and admins always need an email.