Hi Simon-
First, please note that the only 3DConnexion device officially supported (at the moment) in Rhino 5 for Mac is the SpaceNavigator. Other 3DConnexion devices may or may not work as expected.
Second (and this more of a FYI): the way that the 3DConnexion is currently implemented in Rhino 5 for Mac is a legacy of the way that support for these devices was historically implemented in Rhino.
Finally, once we release an official SDK for third-party plugin developers, I would hope that the good people at 3DConnexion will be working to support more of their devices in a more (shall we say?) modern way. Let me stress: the onus is on us as much as them. We are in contact with 3DConnexion (they are likely reading this thread) and are we are all aware of these problems.