No — at this time, you cannot send an email to someone who isn’t a Contact in Event Temple.
To email someone, their email address must already be saved to a Contact profile in your system. This applies to the To, CC, and BCC fields — none of them currently support manually entering and emailing non-contacts.
If you attempt to type a new email address that isn’t tied to an existing Contact, you won’t be able to send the email until you first create a Contact for them.
Workaround: To email someone not currently in your Contact list, create a new Contact first by going to the Contacts tab and clicking New Contact.