Is certainly is, but not the way you do it. The data for each hotspots in the list is loaded per ajax. So the information about the custom fields should be present in the ajax request and then we have to render it in the appropriate position.
What you are trying to do is on our to-do list and it will come with one of the next releases.
Adding Custom Fields to default_infowindowmarker
5 years 1 day ago #32247