Unfortunately Ableton Live does not support Apple's accessibility features and therefore Flexi-deck is unable to identify its UI elements.
Ableton has a feature where you can create keyboard shortcuts that change various parts of its user interface. Therefore FD will be limited to using keystrokes to control Ableton, or click actions that are determined by the position in its window.
There is an undocumented programming interface that's meant to be used for hardware control surfaces. It would appear that this API can be used to provide full control over the entire application and if demand warrants it we may be able to add a special feature to Flexi-deck that uses this interface.