I have tried the Gingerbreak C executable as well. I compiled it successfully on my Mac but no luck rooting. I don't think it is an issue with the SD card partition. The output of Gingerbreak shows that it did indeed find the correct external SD card partition from the /etc/vold.fstab file.
I was able to set up a development system to compile programs for android on my Mac. Unfortunately, I have little to no knowledge of exploits and how to look for them. If someone experienced with rooting can see the source code for the available exploits for other android phones/tablets such as 1) zergRush, and 2) GingerBreak along with the Vizio System files perhaps a way to root the device can be found. Here are the links: