It depends on whether you’re opening a new account or joining an existing one:
Opening a new account: You must use an email address that isn’t already linked to an active Venn account or an unfinished application. If you’ve already started an application with that email, log in to continue it instead of signing up again.
Joining an existing account: Yes, you can use the same email address across multiple active Venn accounts. Ask the owner or admin of the account you want to join to invite you using that email. You can have the same or different roles in each account. This feature is called multi-entity.