You can add one or more USB passthrough devices from an ESXi host to a virtual machine if the physical devices are connected to the host on which the virtual machine runs.
If a USB device is connected to another virtual machine, you cannot add it until that machine releases it.
If you have the Apple Frontpanel Controller device in your environment, you can safely add it to a virtual machine. However, this device has no documented function and no known use. ESXi hosts do not use it and do not provide Xserver functionality for USB passthrough.