I found no Android Homematic app which could connect to Homegear, so there seems to be a difference between Homematic and Homegear for the clients trying to connect.
However, Homematic Manager (I run it using Ubuntu) flawlessly connects and makes my Max!-Devices configurable - however not very intuitive.
Unfortunately I played around so often with my setup that I can no longer reproduce any step. As far as I remember, it was not very difficult to connect Homematic Manager to Homegear. It was something like removing some access restrictions in Homegear, and voila…
Unfortunately, the admin UI of Homegear is not really usable. I need it to set thermostat programs, but for most other aspects (e.g. temperature correction, pairing/connecting devices) I mostly use Homematic Manager.