It wasn't clear to me from the article if this was the POTUS protective detail. I think rentals there would be highly unusual. Our aircrew got stuck going to some Clinton/Gore dog-faced pony show in Monterey in like 1998, and I remember when we flew in to the airport, there was already a staging aircraft there and black vehicles were rolling out the back.
Though I think depending on where, there are SS agents on scene up to a week beforehand doing prep stuff, so if there's no place close like a base where they can borrow a G ride, they probably rent vehicles the same as other gov employees do.