Looks like you are right Andy. No GPU.
Here is from there sight how it works. I do remember reading that it does not cause a performance impact however and my own system experience supports this. I think the key when reading this is it says it does not add anything to the output signal but rather converts it. This would suggest that it makes no difference to the computer or graphics processor.
---------------------------------------
How it Works—A Look Inside the Box
The "magic" of making one display into three happens inside the TripleHead2Go box. The TripleHead2Go takes advantage of the existing graphics processor unit (GPU) within your computer.
Your system GPU renders an ultra-wide image into its frame buffer.
TripleHead2Go uses Matrox patent-pending technology to divide the display information into three display outputs.
These signals are then passed through the three monitor connectors (either standard digital (DVI) or analog (VGA), depending on the version of the product) and to the TripleHead2Go box.
No pixels are added, dropped, scaled, or otherwise changed in this process. TripleHead2Go "magic" preserves all the on-screen information provided by the original monitor signal.
In TripleHead2Go Digital Edition, when an analog input is used, the monitor signal from the computer is first converted to digital data using various techniques to ensure the best possible conversion. These techniques include gain compensation to normalize the signal and phase adjustment to properly interpret either the dual-link input signal or the analog input signal. With the dual-link digital input this conversation is not necessary as you are already in a digital domain.