Yes, you can send bulk invitations from your Contacts and Lead List views. From your stand Salesforce list view on Leads and Contact, users will simply select the records they wish to invite, then click on our out-of-the box-button named "Invite Registrant to a Webinar" > then choose the webinar they wish to invite their Leads/Contacts. 

This action send that persons info to GoToWebinar and the invitee receives the standard GoToWebinar invitation