It appears like most, if not all, of the shells for sale at that auction are not disarmed which is probably good for folks who do that work and don't live too far away from Tallahassee (you know who you are!), but a consideration for bidders who may encounter shipping challenges and extra inerting costs and risks.
As for the 5.1in Schenkl, I have no reason to believe that it could not have been fired from a ship into the Malvern Hill area, but no definitive proof they were used there. It does seem to be in better condition than most, many of which come from wet ground in SC.