Depending on where the probe and heater are located it is possible to create a temperature variance in a room. It is not going to be as extreme as a cage with bottom heat, but if set up right can be a difference of 3-5 degrees.
The trick with heating the whole room is finding the temperature that works.
I know that vpi's book states that they keep their subadult and growing ball pythons at 80-82 degrees without any supplemental heat.