The lack of a response here is quite telling.
“Does an alert now allow a search of any vehicle - vehicles going through a DUI checkpoint, for example - ‘yes’ or ‘no’?”
If a drug dog happens to be there, and it alerts on a vehicle going thru a checkpoint, then yes - there may well be enough probable cause for a search. The threshold for searching a vehicle is low.
Remember, this is NOT a case about warrantless searches of cars. It is a case involving probable cause: would a reasonable person, if they see a drug dog alert on a vehicle, suspect drugs are inside?
The standard is very different for a house, or for a person sitting inside the car.