Currently during Webinar, Panelists can Invite and Remind other Panelists only yet there is no similar option to invite Attendees.
For instance, Panelists might need to invite new and adhoc attendees.
Alternatives to invite adhoc Attendees:
1- Panelists can forward the Webex Webinar invitation Email.
2- Panelists can login to Webex Site and Edit Attendees list.