Alice,
I don't know the answer to your question for certain but I can come up with a reasonable explanation.
Based on what we saw here on this board with the way Disney put the vice clamps on the rental trailer vendors, the vendors (at least some of them) require either you the guest to contact a Disney group to authorize their interaction with your reservation or they get the info from the guest and they arrange it.
Given Disney's track record, I would expect them to require grocery providers like GG or WGS to sign a formal contract with Disney to crystalize their relationship. We can expect some future "delivery charges" passed on from the Disney contract since the grocery vendors are in direct competition with the overpriced, low selection items in the Trading Posts on property. Of course, they MAY allow you to go off-site to buy your own groceries and bring them to your site/cabin but only if you SWEAR that you are bringing them in of your own free volition.
My well-reasoned speculation is that GG needs this to be allowed to come on property and put the groceries in your cabin fridge or in your rental trailer and Disney will eventually inflict a piece of the action on top of your bill. But first they need to data collect. So seriously, I think GG's request would be legitimate to allow them to provide this service to you on Fort property. "Hey there, security dude. My name is Ed and someone named Alice authorized me to go into her cabin and put groceries in the fridge and cupboard."
But I can almost guarantee you that in the future there will be a surcharge added to grocery delivery vendors. So enjoy the fee-free service while you can. You heard it here first....
Bama Ed
PS - I'm going to go into business as a "blockade runner" someday and have a site at the Fort in retirement that I live on full-time. My business will be to deliver golf carts, groceries, baby strollers, and any other items that Disney tries to impose a surcharge, <cough, cough> an "off-site vendor interaction fee", on.
PPS - and no, I'm not paranoid or believe in conspiracies, but I am wearing my tin foil hat...
