It's worth a shot, but I would stop quickly if you start to develop hot spots or pain. Your foot strike is different on a treadmill than on regular ground, and that coupled with the less than forgiving surface of the treadmill could spell disaster I am afraid. Most hiking boots have very little in the way of cushion, which isn't an issue usually because most ground has a little give to it. Your treadmill may not be as forgiving. A while back there was a post by a guy to wore his new hiking boots to Disney world with his family to try and break them in. He ended up with both blisters and foot pain due to walking on concrete without adequate cushion. If I remember correctly he wore the same boots out on a trail hike and didn't have any problems...
Let us know how it works out...