Yes docking stations are supported, but in certain instances the My Cloud isn’t properly recognizing or not properly mounting certain external USB hard drives and docking stations. I’ve experienced this issue in the past. There is previous discussion on some of these USB issues in other threads. In my case I had a Toshiba 1T external USB 3.0 hard drive that wouldn’t properly mount, the solution was to delete the partition on that Toshiba external hard drive, create a new one and then reformat the drive. I too had problems with a generic docking station not working with one particular hard drive (a Seagate 1T drive), yet worked fine with a WD Green 500GB hard drive when connected to the My Cloud.
Does the My Cloud indicate the docking station is attached but shows 0K via the USB icon within the My Cloud Dashboard? If so the My Cloud is seeing the drive but failing to mount it properly.
You can see some of my experiences with this particular USB issue in the following thread.