Yes, but the maximum number of USB hubs you can daisy chain is 5 in series. Some of the USB ports in the dock are chained through 2 USB hubs, and including the USB hub in the PC, you might get near this limit for some of the downstream USB ports on the 2nd dock.
If you just want to add 2 more heads, you would probably be better off with a USB to dual video USB adapter, rather than a dock. There are a few of these in the DisplayLink shop:
http://www.displaylink.com/shop/adapters
Wim