Yes, you can bulk upload a list of contacts that are not in Salesforce yet to a Flow via a .CSV file. Groove will simultaneously create the contacts in Salesforce and add them to the Flow.
You’ll want to choose the CSV Lookup tab when you go to add people to your Flow. Groove will first search for any Contacts/Leads in your CSV who do exist in Salesforce, then given you the option to create new Contacts/Leads for the people in the CSV who do not exist in Salesforce yet.
This feature is called Direct Import, and it needs to be set up by an admin. If you’re an admin and you do not see the Direct Import setting in Manage My Org, please reach out to your CSM or the Clari support team to have this feature enabled for your org.