Is Full page screenshot option available in Zipboard

Yes, It is available for the Web URL file type.

When you add Web URL to the project and click on Review, It navigates to Review Board when you click on the camera, it shows 2 options 

1. Visible page: Capture only visible page

2.Full page: Capture Full page by scroll down till the end of the page.

Once captured will navigate to Review Board, you can annotate it.