You can't do this as a drawable or a view background, but you can theme your activity to make the wallpaper or live wallpaper show through.
<style name="MyTheme" parent="@android:style/Theme.Black.NoTitleBar.Fullscreen">
<item name="android:windowBackground">@android:color/transparent</item>
<item name="android:colorBackgroundCacheHint">@null</item>
<item name="android:windowShowWallpaper">true</item>
</style>
You can use any theme as the parent. Put this in your styles resource and set this theme for the activity in the manifest.