@Drakat it's fins to use a common +VIN wire for the fans and hot end heaters, and also the Z probe if it is an inductive sensor that needs a VIN feed.
A common ground for the Z probe and the Z endstop is also OK.
A problem arises if the tool head board assumes that the thermistor also uses the common ground connection. In line with good practice, Duets boards use separate analog and digital grounds in order to get good signal integrity when reading the thermistors. The analog ground is called VSSA. Duets also provide a PTC fuse between VSSA and ground, because shorts between hot end heaters and thermistors are a common occurrence. So if your tool head board assumes a common ground with the thermistor, you have two choices:
Run a separate VSSA wire between the tool head and the Duet;
Use the common ground and don't connect to the VSSA pin at the Duet end. You will get less accurate temperature readings and you will lose the protection of the fuse.
