Does GeometryEngine operations need spatialreference attribute defined for the input geometries ?
I have tried polygon intersection, where both the input geometries(and their vertex points) does not have any spatial reference defined which yielded no results whereas the polygon geometries should be intersecting
A spatial reference is not required for most of the GeometryEngine methods. For the Project and geodesic methods, you must have a spatial reference defined. The other methods use the tolerance of the spatial reference to determine if points that are close to each other should be considered equal. If you don't have a spatial reference defined, then a default tolerance is used.
When you say that you tried GeometryEngine.Intersection with geometries that don't have a spatial reference, what do you mean that it yielded no results? Did it return an empty geometry, a null geometry, or throw an exception? It should work.