For “pure” Android application development you need to use the Android development environment and I think this probably limits you mostly making to RFCONN links (so good for self-built hardware). You can also rely on the built-in support for things like HID devices and A2DP headphones (e.g. you can’t drive the low level layer directly but you can stream sound to them).
However… you do also have the source! That is far more powerful than any SDK.
If you really want to do low-level BT work on Android/DB410c then you can build from source and add new features to the platform itself (using the existing features for reference on how to do it).