ubiquity offers essentially a wifi module called the bullet that is essentially just a standard wireless network for long ranges and high data transfer rates. Picture clarity and resolution are very important because the images will be analyzed using openCV to find various glyphs on the ground. This is the reason why we decided not to go with video and pictures instead. Assuming we went through USB, are you saying the arduino serial communications would bottleneck the process? There are publically available serial protocols for DSLRs I believe, but I imagine either the arduino or the ethernet shield (which the bullet plugs into), would slow things down majorly.
The flow I should have put in the post, which I don't even know if it is compatible:
Camera>USB>Arduino serial port>ethernet shield>bullet wifi device>ground antenna>ground computer