Yes, your employees (or team members) have to signup to refer. However, it is not mandatory for them to upload their contacts on Hachi - read more about that here.
Hachi sends a weekly mail to your employees suggesting friends they can refer for the jobs posted by you - there is a ‘Refer’ button in the email, they can refer from the email itself. Making it one-click for them to refer. No need to login or to download any app.