Bindings that are only stored in the addons folder are not visible in the list.
You can check whether it is working in the Karaf Console. Run bundle:list | grep Homematic to get the binding’s state. If it shows “active” then everything is fine. If the state is “installed”, you can try to start it with bundle:start <number>. You will see an error message if it can’t be started.
BTW: the test version of the binding requires a snapshot version. It won’t run on 3.0.1.