I work at Brinks. Yes it is SOP anytime the garage door is open we will have at least one gaurd with a weapon upholstered or a long gun.
I would like to know how it makes them an easy target? We have enough awareness to notice people close enough to pose a threat. Well unless we have some snipers camped out on some roofs!
Yes you are correct, I missed that part of the OPs story. Exit/Entry into any depository guards are required to have weapon in hand and at the ready until the gates or doors are closed.