It shows with their documentation, it’s confusing, obscure and outdated.
I can confirm that the above guide: Creating HTML5 Advertisements for Sizmek in Tumult Hype seems to have worked correctly as of April 2019.
I just used a regular ‘clickthrough’ in the Actions > Sizmek panel attached to a transparent shape layer - as the client needs to be able to repoint the ad to different URLs in the future this works great.
All seems good.