Do I need Zendesk in order to use CXBOX BROADCAST?

Yes, you need to subscribe at least Zendesk Suite Professional in order to use BROADCAST. The reason is BROADCAST is deployed by plugging with Zendesk via Sunshine Conversations or Conversation API module bundled together with Zendesk Suite Professional Plan.

By fully integrating with Zendesk, you will be able to handle a full-loop customer engagement tasks efficiently.