How are the colliders for interactions set in Tobii Pro VR Analytics? Is it per polygon? Or can you group the collider for several polygons?

VR Integration Tobii Pro
This is entirely up to the creator of the VR. Typically, the colliders are created to be a single object, with a single surface, a full polygon, or a plane in front many polygons (e.g. a shelf collider covering all the products on the top shelf). These effectively become the AOIs (or Objects of Interest in 3D) that all metrics are reported against, so the precise level of detail depends somewhat on the research question and how you want to analyze the data. There is currently no concept of an Object Group in Tobii Pro VR Analytics.