There are multiple ways to preview in Event Hub. Here is a good example
The preview page on the Design Centre os for design preview only. For example, tickets with barcodes as part of the design will show a standard generic barcode.
You can preview in many ways.
VIP Preview
During the send process, you are able to fully preview your send EDM in the step prior to the send. This can be done with both Invites and details EDMs.
Commercial EDM send
Like the VIP you are able to preview the send and approve prior to any send during the communication process
You can create, build and preview tickets for single assets on the ticketing page. This is suggested to ensure all data for the event is injected into the ticket.