Is it possible to use the Geospatial API in a location covered by Google Earth but not by Street View?
A visual part of a geospatial model is crucial. You need both, a visual data (panoramic images of streets + GE imagery) and sensor data (GPS) to determine precise location. Google Earth, however, is only based on satellite imagery and aerial photography. As you know, Street View is an integral part of Google Maps, and you cannot stop using Street View when creating GeoTracking AR app because neural engine of Geospatial API needs it to identify environmental images.
If you are interested in how a similar technology works in ARKit, read this post.
However, there is always a workaround. You can use a simplified (and therefore less accurate) version of geospatial anchor that allows you to accommodate your models using just latitude and longitude.