Yes you can do that (disable the emails when adding staff) but i think you will have to install ghost from source, edit the proper files and then deploy you custom build.
A workaround: You can just create a bunch of emails on gmail or hotmail or yahoo or something so when creating the ghost accounts the email will be received by an account you control.
A more elegant solution would be to create a number of email aliases that point to your personal or business email and create the ghost accounts with those aliases.
For example lets say your email is firstname.lastname@example.org you could enter your cpanel or whatever you use and create a bunch of email aliases. All of them will point to email@example.com
If you have 3 interviewees you need to give access to ghost admin those emails aliases can be:
Remember email aliases are not real email accounts in the sense that you cant use them to send email. But if someone (the ghost api or mailgun) send an email to one email alias you will always catch that email on your personal email.
That way you can create ghost accounts and it does not matter the accounts will receive an email because the emails are aliases that point to your personal or business email.
You can share to the interviewers their username and password (for their ghost accounts) by whatsapp or an email written by yourself.