IGEL units will pass through USB devices for the View session. Its possible to block this from a UMS policy whilst also having the granularity of allowing USB devices that are required such as headsets. Blocking a USB device is fairly straight forward, open the UMS console and login

Choose the policy required, in this example a policy called ‘VMware View Appliance Mode’

Expand Sessions - Horizon Client - Horizon Client Global - USB Redirection. Enable redirection if it is not already set. Im this example USB headset were required but Mass Storage devices were not permitted. Add the required rule to ‘Class Rules’ either allow or deny the family of devices. If you require a specific device rule that fails under a family, ie a particualar USB storage device used for an application but you still want to block all other storage devices, add this under ‘Device Rules’. Plug the required device into a PC and find the Vendor ID and Product ID information.

To find the Vendor ID follow this blog, you need the Hex value

http://thecurlybrace.blogspot.co.uk/2010/07/how-to-find-usb-device-vendor-and.html