You can insert custom data into the custom payload field(s) inside a hotspot or an overlay element. Set up your hotspot or button action as you normally would, but toggle on Add custom payload data. This will allow you to then add keys & values as your primary action. This could be useful when looking to add additional tracking to your video.
When you listen to the interactive events in the Vimeo Player API (see documentation) you will be able to see the custom data surfaced and use it in whatever way you like.