All snakes have the potential to eat other snakes. There have been recorded instances of this happening with hogs. I personally new someone about ten years ago whose cornsnake ate another corn (I believe alot of this had to do with his poor feeding practices). Even though this is rare, you shouldn't risk it.
Also, corns and hogs have slightly different enviornmantal needs. For example, hogs need less humidity than corns. If you mix species you are just asking for trouble.
Bottem line, if you can't afford or don't have space for another tank, then don't get another snake. There are many inexpensive housing options and neither hogs nor corns need alot of space, so if you get a hog, give it its own home.
Jim