i replaced my rearend this last weekend and noticed when the brake like splints on the axle there what looked to be like a piece of a rubber vent line on both my axles that had been cut just wondering if that was a vent line for the axle or what it was

 

Yep, it vents the axle. The rubber line should be run up as high as you can get it and then face it downward, helps keep the dirt out. I think there is a breather on the end of mine.