you can make a harvester spawn with the harvester vehicle factory if you use the factory in the map and dont you kismet it will re-spawn after getting destroyed as for the 0,0,0 spawning you cant turn that off just yet with out destroying the refinery
there is one other method by having a spawning platform @ 0,0,0 and having the map above it or away from it (but this would mean the harvester would be looking for a path all the time and could add too lag)