https://github.com/tpurtell/AndroidHockeyApp
It includes an additional class, TraceWriter, which allows you to log exceptions that come from .NET into HockeyApp. Exceptions are reported to HockeyApp and are properly grouped. You will see both java and c# based exceptions.
The tricky thing is that you have to integrate it into how you work with Tasks, since the .NET uncaught task exception only reports when a Task has an exception and is finalized. I never saw this happen, so I suspect some part of the framework is holding onto a reference.
There are some more details in the README on github.