A bad bearing would have to be causing a lot of harsh vibration to kill a GOOD rear main seal. If the seal was already on its way out there would still have to be a significant amount of vibration to finish the job.... or you could starve the seals of oil to help kill them off quickly; the wipers or lips ride on a thin sacrificial layer of oil (that's right, an intentional, itty bitty leak) which lubricates and actually helps prevent any larger volume from flowing through (they're directional for a reason too.
). Now, if the thrust washer is shot and there's significant lateral movement it may contribute further.
The oil pan and gallery seals would not be affected the subtle vibration of a bad main bearing or three.
As stated before, the rear main can be done without pulling the engine... it's still a decent amount of work but not $3000 worth.