In general it is not suggested that you layer external USB hubs of any variety. The RAVEN contains 1 USB port which requires connection to the computer. It's advised that you plug this straight into your computer.
Typically a Mac pro has two USB buses, one in the front and one in the back. The multiple ports are instances on each bus, so they share power and bandwidth. Hubs work well with low-power and low-bandwidth devices, but are unstable with high-power or high-bandwidth. Our USB hub has an outboard power supply to make sure it has all the current it needs, but bandwidth is determined upstream in your computer. It's possible to add additional PCI cards with USB buses to some Macs and most PCs to provide more bandwidth if you need it.