PPH and DLH guests are 100% allowed and expected to use that entrance.
Offsite guests are not allowed to use it at park opening.
OK, when the new system is up and running , there will be two security check areas, the current one to enter DCA, and then the hallway to go to Downtown Disney by Sephora.
Since this will be a NEW Security Check, there are no known rules. IMHO, Disney is going to play it by ear, but I can easily see them limit the use, at least in the morning to just GCH guests to go through security to get into Downtown Disney. As they say, everything is subject to change at Disney. I was in the park this afternoon, and there is a large set of security gates being built between the ESPN Zone and the Earl of Sandwich, which is where Disney wants both the PPH and DH guests to go to enter the secure area.
So to keep the lines down for GCH guests,who have no other real option, unless they walk to the PPH and then head north, to enter the parks and Downtown Disney. They are already going to have a lot of upset guests due to the pool refurb and the room construction/refurb.
So on January 1st, Disney revises their policy of using the GCH entrances, in the morning, only GCH guests can use either entrance, after the morning rush, they can open it up to other people, such as those having a meal at the GCH. There is no more secret exit into DtD next to the La Brea Bakery,as it will be gated off.
Of course, all three Hotel Guests will still get the Extra Magic Hour, but will be expected to enter the parks from the Main Ticket Booth area (Esplanade).
Things are changing, and they are working hard to get it done by the end of next week...
Only time will tell what Disney comes up with for the rules for the new system.