DesktopAssetManager is used both on desktop and android. It is a misnomer!
these might be related:
I have not read those threads thoroughly so I am not sure what actually causes the UnsupportedOperationException on android when loading Ogg files outside of android’s assets directory (‘src/main/assets’ ,located in your app’s project) but it works fine with other assets. It probably is a limitation in android NativeVorbisLoader.
Note:
I have recently updated jme3-android to use OGGLoader from jme3-jogg instead of NativeVorbisLoader for loading ogg audio which might solve this issue.
You need to build the engine from the master branch if you are interested to give it a try. Please let me know if it solves the issue.