If you do a search here for oil systems, there are tons of posts and schematics on the system. My understanding is the two pumps (the oil pump is really two pumps) are somewhat separate. The pressure pump circulates oil from the tank to the internals. The scavenge pump sucks the oil from the case, and sends it out to the thermostat, cooler and back to the tank.
http://forums.pelicanparts.com/911-engine-rebuilding-forum/632726-911-3-0l-sc-oil-cooler-system.html