here is a note on how to mount a usb key or get it recognized by the hypervisor system (esxi system) and not use it to passthru to a guest on the system.
bad news, it only works with FAT16 file systems.
only USB storage devices formatted with FAT16 can be accessed in the ESXi shell and is applicable to both ESXi 4.1 and 5.0.
Step 1 - Login to ESXi Shell via SSH and disable the USB Arbitrator service (this is automatically enabled by default to allow pass-through of USB devices to your VMs) using the following command: /etc/init.d/usbarbitrator stop
Step 2 - Plug-in your USB device to your ESXi host and you can verify by using the two ESXCLI commands: verifying the storage device using the command: esxcli storage core device list | grep -i usb or viewing the mounted filesystems using the command: esxcli storage filesystem list
Step 3 - Lastly, after you verify the USB device can be seen by the ESXi host, you can of course browse and access your USB device by looking under /vmfs/volumes/
Te re-enable pass-through of USB devices to your VMs, you just need to start the usbarbitrator service. - See more at: