Hi Berkay,
Radek from the GoodData Technical team here!
When it comes to Hotjar and Fullstory, they both have the limitation of having to have control over the source code of whatever page is being displayed through an iframe - this comes from the security properties of iframes themselves, and unfortunately prevents both tools from tracking properly.
From the GoodData side, an iframe Dashboard sends out events for some interactions - these are possible to be captured using an eventListener. I would suggest testing this out and seeing if the events are sufficient for tracking; outside of that, I'm afraid there isn't much more that can be done through an iframe.
Hope this helps!