Short of hacking the Android SDK into your Java project, are there any Java clients that can consume and work with ArcGIS Server services? e.g. create Feature Sets, Geometries, perform Queries/Geoprocess tasks, etc.. 
Similar to what you can use the Javascript or ObjC SDK's. Though I don't need to visualize, only interact with the services. 
The closest thing I've seen is the Geometry API:
<https://github.com/Esri/geometry-api-java>
No, I don't want ArcObjects or any SDK that requires some $$license.