The blower pulley's center spindle threads into the crank pulley and there shouldn't be any reason to have oil leaking from there when you removed it. None of the pulleys (with the exception of the older JDM pulleys with the braces) provide anything to fill in the center of the crank pulley after the blower pulley's removal.
If you have oil leaking from there I would say look at your front main seal as even the crank pulley bolt wouldn't cause oil to leak (there's no oil that would enter the crank and be able to leak from that bolt hole).