“Good. Announce your plan well in advance and Mr. FBI will be glad to see that you all board the bus to the federal lockup located at Eglin AFB, or if you’re really, really lucky... Guantanamo Bay, Cuba.”
The FBI clowns don’t guard Area51. It’s the military and Wackenhut.
If the USAF Security Forces are expecting several tens of thousands of visitors all marshaling outside their immediate area of responsibility, they’d be foolish not to ask the feds to cordon off that area.
And it makes sense as Area 51 is very remote. You can’t just rush it from a mile away. There’s a lot of rough terrain to cover and a lot of logistics will be needed. Like organizing the Boston Marathon or a central American migrant ‘caravan’.