As much as I hate quads, they are a much more viable option for military use. Driving w/ NODS on an ATV at night is tough enough, on a bike it would be hell, plus a quad allows you to carry your ruck, extra gear, batteries, ammo, food, water, etc... Not to mention that you can add your squad weapon of choice and have a very mobile platform.
I supply the military (via one of my customers) a fair amount of ATV and motorcycle accessories and consumables. Kawasaki is the largest segment, followed by Polaris and Yamaha. But there's a little bit of everything.
Here's a link to some more pictures of the Christini Military bikes used by Special Forces. http://thebrigade.thechive.com/2012/11/29/christini-sf-dirt-bike-with-awd-11-photos/