Some of those pumps (maybe all) have a float (or some other means) to disable the furnace when the resivour fills too much. I comment on whether it looks like it is set up to do that (extra thermostat type wires going back to the furnace) or not. They can also install a floodstop device if the pump does not have the shut-off capability.
Edit: Here is a link to a pump. It looks like the overflow switch is an option.
http://www.fieldcontrols.com/pdfs/CONDENpump.PDF