I feel you. Let me share a screenshot of the current state of linux driver: It doesn't look this driver was subject of any changes since mid 90's so it might be a problem on 3dcoat side in this particular case after all.
3D mouse viewport navigation doesn't seem to be working on Linux while buttons do. Switching to new api doesn't seem to work either, after clicking apply the dialog blinks and reverts back to former settings. Tested with 3DConnexion 3DX-700059 Spacemouse Compact 3D Mouse. 3DxWareUNIX = V1.8.0 Device = SpaceNavigator Firmware = V4.35